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Network Working Group P. Holbrook Request for Comments: 1244 CICNet FYI: 8 J. Reynolds

                                                             July 1991
                       Site Security Handbook

Status of this Memo

 This handbook is the product of the Site Security Policy Handbook
 Working Group (SSPHWG), a combined effort of the Security Area and
 User Services Area of the Internet Engineering Task Force (IETF).
 This FYI RFC provides information for the Internet community.  It
 does not specify an Internet standard.  Distribution of this memo is

Contributing Authors

 The following are the authors of the Site Security Handbook.  Without
 their dedication, this handbook would not have been possible.
 Dave Curry (Purdue University), Sean Kirkpatrick (Unisys), Tom
 Longstaff (LLNL), Greg Hollingsworth (Johns Hopkins University),
 Jeffrey Carpenter (University of Pittsburgh), Barbara Fraser (CERT),
 Fred Ostapik (SRI NISC), Allen Sturtevant (LLNL), Dan Long (BBN), Jim
 Duncan (Pennsylvania State University), and Frank Byrum (DEC).

Editors' Note

 This FYI RFC is a first attempt at providing Internet users guidance
 on how to deal with security issues in the Internet.  As such, this
 document is necessarily incomplete.  There are some clear shortfalls;
 for example, this document focuses mostly on resources available in
 the United States.  In the spirit of the Internet's "Request for
 Comments" series of notes, we encourage feedback from users of this
 handbook.  In particular, those who utilize this document to craft
 their own policies and procedures.
 This handbook is meant to be a starting place for further research
 and should be viewed as a useful resource, but not the final
 authority.  Different organizations and jurisdictions will have
 different resources and rules.  Talk to your local organizations,
 consult an informed lawyer, or consult with local and national law
 enforcement.  These groups can help fill in the gaps that this
 document cannot hope to cover.

Site Security Policy Handbook Working Group [Page 1] RFC 1244 Site Security Handbook July 1991

 Finally, we intend for this FYI RFC to grow and evolve.  Please send
 comments and suggestions to:

Table of Contents

1. Introduction…………………………………………….. 3 1.1 Purpose of this Work…………………………………….. 3 1.2 Audience……………………………………………….. 3 1.3 Definitions…………………………………………….. 4 1.4 Related Work……………………………………………. 4 1.5 Scope………………………………………………….. 4 1.6 Why Do We Need Security Policies and Procedures?……………. 5 1.7 Basic Approach………………………………………….. 7 1.8 Organization of this Document…………………………….. 7 2. Establishing Official Site Policy on Computer Security……….. 9 2.1 Brief Overview………………………………………….. 9 2.2 Risk Assessment…………………………………………. 10 2.3 Policy Issues…………………………………………… 13 2.4 What Happens When the Policy Is Violated…………………… 19 2.5 Locking In or Out……………………………………….. 21 2.6 Interpreting the Policy………………………………….. 23 2.7 Publicizing the Policy…………………………………… 23 3. Establishing Procedures to Prevent Security Problems…………. 24 3.1 Security Policy Defines What Needs to be Protected………….. 24 3.2 Identifing Possible Problems……………………………… 24 3.3 Choose Controls to Protect Assets in a Cost-Effective Way……. 26 3.4 Use Multiple Strategies to Protect Assets………………….. 26 3.5 Physical Security……………………………………….. 27 3.6 Procedures to Recognize Unauthorized Activity………………. 27 3.7 Define Actions to Take When Unauthorized Activity is Suspected.. 29 3.8 Communicating Security Policy…………………………….. 30 3.9 Resources to Prevent Security Breaches…………………….. 34 4. Types of Security Procedures………………………………. 56 4.1 System Security Audits…………………………………… 56 4.2 Account Management Procedures…………………………….. 57 4.3 Password Management Procedures……………………………. 57 4.4 Configuration Management Procedures……………………….. 60 5. Incident Handling………………………………………… 61 5.1 Overview……………………………………………….. 61 5.2 Evaluation……………………………………………… 65 5.3 Possible Types of Notification……………………………. 67 5.4 Response……………………………………………….. 71 5.5 Legal/Investigative……………………………………… 73 5.6 Documentation Logs………………………………………. 77 6. Establishing Post-Incident Procedures………………………. 78 6.1 Overview……………………………………………….. 78 6.2 Removing Vulnerabilities…………………………………. 78 6.3 Capturing Lessons Learned………………………………… 80

Site Security Policy Handbook Working Group [Page 2] RFC 1244 Site Security Handbook July 1991

6.4 Upgrading Policies and Procedures…………………………. 81 7. References………………………………………………. 81 8. Annotated Bibliography……………………………………. 83 8.1 Computer Law……………………………………………. 84 8.2 Computer Security……………………………………….. 85 8.3 Ethics…………………………………………………. 91 8.4 The Internet Worm……………………………………….. 93 8.5 National Computer Security Center (NCSC)…………………… 95 8.6 Security Checklists……………………………………… 99 8.7 Additional Publications………………………………….. 99 9. Acknlowledgements…………………………………………101 10. Security Considerations…………………………………..101 11. Authors' Addresses……………………………………….101

1. Introduction

1.1 Purpose of this Work

 This handbook is a guide to setting computer security policies and
 procedures for sites that have systems on the Internet.  This guide
 lists issues and factors that a site must consider when setting their
 own policies.  It makes some recommendations and gives discussions of
 relevant areas.
 This guide is only a framework for setting security policies and
 procedures.  In order to have an effective set of policies and
 procedures, a site will have to make many decisions, gain agreement,
 and then communicate and implement the policies.

1.2 Audience

 The audience for this work are system administrators and decision
 makers (who are more traditionally called "administrators" or "middle
 management") at sites.  This document is not directed at programmers
 or those trying to create secure programs or systems.  The focus of
 this document is on the policies and procedures that need to be in
 place to support any technical security features that a site may be
 The primary audience for this work are sites that are members of the
 Internet community.  However, this document should be useful to any
 site that allows communication with other sites.  As a general guide
 to security policies, this document may also be useful to sites with
 isolated systems.

Site Security Policy Handbook Working Group [Page 3] RFC 1244 Site Security Handbook July 1991

1.3 Definitions

 For the purposes of this guide, a "site" is any organization that
 owns computers or network-related resources.  These resources may
 include host computers that users use, routers, terminal servers,
 PC's or other devices that have access to the Internet.  A site may
 be a end user of Internet services or a service provider such as a
 regional network.  However, most of the focus of this guide is on
 those end users of Internet services.
 We assume that the site has the ability to set policies and
 procedures for itself with the concurrence and support from those who
 actually own the resources.
 The "Internet" is those set of networks and machines that use the
 TCP/IP protocol suite, connected through gateways, and sharing a
 common name and address spaces [1].
 The term "system administrator" is used to cover all those who are
 responsible for the day-to-day operation of resources.  This may be a
 number of individuals or an organization.
 The term "decision maker" refers to those people at a site who set or
 approve policy.  These are often (but not always) the people who own
 the resources.

1.4 Related Work

 The IETF Security Policy Working Group (SPWG) is working on a set of
 recommended security policy guidelines for the Internet [23].  These
 guidelines may be adopted as policy by regional networks or owners of
 other resources.  This handbook should be a useful tool to help sites
 implement those policies as desired or required.  However, even
 implementing the proposed policies isn't enough to secure a site.
 The proposed Internet policies deal only with network access
 security.  It says nothing about how sites should deal with local
 security issues.

1.5 Scope

 This document covers issues about what a computer security policy
 should contain, what kinds of procedures are need to enforce
 security, and some recommendations about how to deal with the
 problem.  When developing a security policy, close attention should
 be made not only on the security needs and requirements of the local
 network, but also the security needs and requirements of the other
 interconnected networks.

Site Security Policy Handbook Working Group [Page 4] RFC 1244 Site Security Handbook July 1991

 This is not a cookbook for computer security.  Each site has
 different needs; the security needs of a corporation might well be
 different than the security needs of an academic institution.  Any
 security plan has to conform to the needs and culture of the site.
 This handbook does not cover details of how to do risk assessment,
 contingency planning, or physical security.  These things are
 essential in setting and implementing effective security policy, but
 this document leaves treatment of those issues to other documents.
 We will try to provide some pointers in that direction.
 This document also doesn't talk about how to design or implement
 secure systems or programs.

1.6 Why Do We Need Security Policies and Procedures?

 For most sites, the interest in computer security is proportional to
 the perception of risk and threats.
 The world of computers has changed dramatically over the past
 twenty-five years.  Twenty-five years ago, most computers were
 centralized and managed by data centers.  Computers were kept in
 locked rooms and staffs of people made sure they were carefully
 managed and physically secured.  Links outside a site were unusual.
 Computer security threats were rare, and were basically concerned
 with insiders: authorized users misusing accounts, theft and
 vandalism, and so forth.  These threats were well understood and
 dealt with using standard techniques: computers behind locked doors,
 and accounting for all resources.
 Computing in the 1990's is radically different.  Many systems are in
 private offices and labs, often managed by individuals or persons
 employed outside a computer center.  Many systems are connected into
 the Internet, and from there around the world: the United States,
 Europe, Asia, and Australia are all connected together.
 Security threats are different today.  The time honored advice says
 "don't write your password down and put it in your desk" lest someone
 find it.  With world-wide Internet connections, someone could get
 into your system from the other side of the world and steal your
 password in the middle of the night when your building is locked up.
 Viruses and worms can be passed from machine to machine.  The
 Internet allows the electronic equivalent of the thief who looks for
 open windows and doors; now a person can check hundreds of machines
 for vulnerabilities in a few hours.
 System administrators and decision makers have to understand the
 security threats that exist, what the risk and cost of a problem

Site Security Policy Handbook Working Group [Page 5] RFC 1244 Site Security Handbook July 1991

 would be, and what kind of action they want to take (if any) to
 prevent and respond to security threats.
 As an illustration of some of the issues that need to be dealt with
 in security problems, consider the following scenarios (thanks to
 Russell Brand [2, BRAND] for these):
  1. A system programmer gets a call reporting that a

major underground cracker newsletter is being

      distributed from the administrative machine at his
      center to five thousand sites in the US and
      Western Europe.
      Eight weeks later, the authorities call to inform
      you the information in one of these newsletters
      was used to disable "911" in a major city for
      five hours.
  1. A user calls in to report that he can't login to his

account at 3 o'clock in the morning on a Saturday. The

      system staffer can't login either.  After rebooting to
      single user mode, he finds that password file is empty.
      By Monday morning, your staff determines that a number
      of privileged file transfers took place between this
      machine and a local university.
      Tuesday morning a copy of the deleted password file is
      found on the university machine along with password
      files for a dozen other machines.
      A week later you find that your system initialization
      files had been altered in a hostile fashion.
  1. You receive a call saying that a breakin to a government

lab occurred from one of your center's machines. You

      are requested to provide accounting files to help
      trackdown the attacker.
      A week later you are given a list of machines at your
      site that have been broken into.
  1. A reporter calls up asking about the breakin at your

center. You haven't heard of any such breakin.

      Three days later, you learn that there was a breakin.
      The center director had his wife's name as a password.

Site Security Policy Handbook Working Group [Page 6] RFC 1244 Site Security Handbook July 1991

  1. A change in system binaries is detected.
      The day that it is corrected, they again are changed.
      This repeats itself for some weeks.
  1. If an intruder is found on your system, should you

leave the system open to monitor the situation or should

      you close down the holes and open them up again later?
  1. If an intruder is using your site, should you call law

enforcement? Who makes that decision? If law enforcement asks

      you to leave your site open, who makes that decision?
  1. What steps should be taken if another site calls you and says

they see activity coming from an account on your system? What

      if the account is owned by a local manager?

1.7 Basic Approach

 Setting security policies and procedures really means developing a
 plan for how to deal with computer security.  One way to approach
 this task is suggested by Fites, et. al. [3, FITES]:
  1. Look at what you are trying to protect.
  2. Look at what you need to protect it from.
  3. Determine how likely the threats are.
  4. Implement measures which will protect your assets in a

cost-effective manner.

  1. Review the process continuously, and improve things every time

a weakness is found.

 This handbook will concentrate mostly on the last two steps, but the
 first three are critically important to making effective decisions
 about security.  One old truism in security is that the cost of
 protecting yourself against a threat should be less than the cost
 recovering if the threat were to strike you.  Without reasonable
 knowledge of what you are protecting and what the likely threats are,
 following this rule could be difficult.

1.8 Organization of this Document

 This document is organized into seven parts in addition to this
 The basic form of each section is to discuss issues that a site might
 want to consider in creating a computer security policy and setting
 procedures to implement that policy.  In some cases, possible options
 are discussed along with the some of the ramifications of those

Site Security Policy Handbook Working Group [Page 7] RFC 1244 Site Security Handbook July 1991

 choices.  As far as possible, this document tries not to dictate the
 choices a site should make, since these depend on local
 circumstances.  Some of the issues brought up may not apply to all
 sites.  Nonetheless, all sites should at least consider the issues
 brought up here to ensure that they do not miss some important area.
 The overall flow of the document is to discuss policy issues followed
 by the issues that come up in creating procedures to implement the
 Section 2 discusses setting official site policies for access to
 computing resources.  It also goes into the issue of what happens
 when the policy is violated.  The policies will drive the procedures
 that need to be created, so decision makers will need to make choices
 about policies before many of the procedural issues in following
 sections can be dealt with.  A key part of creating policies is doing
 some kind of risk assessment to decide what really needs to be
 protected and the level of resources that should be applied to
 protect them.
 Once policies are in place, procedures to prevent future security
 problems should be established.  Section 3 defines and suggests
 actions to take when unauthorized activity is suspected.  Resources
 to prevent secruity breaches are also discussed.
 Section 4 discusses types of procedures to prevent security problems.
 Prevention is a key to security; as an example, the Computer
 Emergency Response Team/Coordination Center (CERT/CC) at Carnegie-
 Mellon University (CMU) estimates that 80% or more of the problems
 they see have to do with poorly chosen passwords.
 Section 5 discusses incident handling: what kinds of issues does a
 site face when someone violates the security policy.  Many decisions
 will have to made on the spot as the incident occurs, but many of the
 options and issues can be discussed in advance.  At very least,
 responsibilities and methods of communication can be established
 before an incident.  Again, the choices here are influenced by the
 policies discussed in section 2.
 Section 6 deals with what happens after a security violation has been
 dealt with.  Security planning is an on-going cycle; just after an
 incident has occurred is an excellent opportunity to improve policies
 and procedures.
 The rest of the document provides references and an annotated

Site Security Policy Handbook Working Group [Page 8] RFC 1244 Site Security Handbook July 1991

2. Establishing Official Site Policy on Computer Security

2.1 Brief Overview

 2.1.1  Organization Issues
    The goal in developing an official site policy on computer
    security is to define the organization's expectations of proper
    computer and network use and to define procedures to prevent and
    respond to security incidents.  In order to do this, aspects of
    the particular organization must be considered.
    First, the goals and direction of the organization should be
    considered.  For example, a military base may have very different
    security concerns from a those of a university.
    Second, the site security policy developed must conform to
    existing policies, rules, regulations and laws that the
    organization is subject to.  Therefore it will be necessary to
    identify these and take them into consideration while developing
    the policy.
    Third, unless the local network is completely isolated and
    standalone, it is necessary to consider security implications in a
    more global context.  The policy should address the issues when
    local security problems develop as a result of a remote site as
    well as when problems occur on remote systems as a result of a
    local host or user.
 2.1.2  Who Makes the Policy?
    Policy creation must be a joint effort by technical personnel, who
    understand the full ramifications of the proposed policy and the
    implementation of the policy, and by decision makers who have the
    power to enforce the policy.  A policy which is neither
    implementable nor enforceable is useless.
    Since a computer security policy can affect everyone in an
    organization, it is worth taking some care to make sure you have
    the right level of authority in on the policy decisions.  Though a
    particular group (such as a campus information services group) may
    have responsibility for enforcing a policy, an even higher group
    may have to support and approve the policy.
 2.1.3  Who is Involved?
    Establishing a site policy has the potential for involving every
    computer user at the site in a variety of ways.  Computer users

Site Security Policy Handbook Working Group [Page 9] RFC 1244 Site Security Handbook July 1991

    may be responsible for personal password administration.  Systems
    managers are obligated to fix security holes and to oversee the
    It is critical to get the right set of people involved at the
    start of the process.  There may already be groups concerned with
    security who would consider a computer security policy to be their
    area.  Some of the types of groups that might be involved include
    auditing/control, organizations that deal with physical security,
    campus information systems groups, and so forth.  Asking these
    types of groups to "buy in" from the start can help facilitate the
    acceptance of the policy.
 2.1.4  Responsibilities
    A key element of a computer security policy is making sure
    everyone knows their own responsibility for maintaining security.
    A computer security policy cannot anticipate all possibilities;
    however, it can ensure that each kind of problem does have someone
    assigned to deal with it.
    There may be levels of responsibility associated with a policy on
    computer security.  At one level, each user of a computing
    resource may have a responsibility to protect his account.  A user
    who allows his account to be compromised increases the chances of
    compromising other accounts or resources.
    System managers may form another responsibility level: they must
    help to ensure the security of the computer system.  Network
    managers may reside at yet another level.

2.2 Risk Assessment

 2.2.1  General Discussion
    One of the most important reasons for creating a computer security
    policy is to ensure that efforts spent on security yield cost
    effective benefits.  Although this may seem obvious, it is
    possible to be mislead about where the effort is needed.  As an
    example, there is a great deal of publicity about intruders on
    computers systems; yet most surveys of computer security show that
    for most organizations, the actual loss from "insiders" is much
    Risk analysis involves determining what you need to protect, what
    you need to protect it from, and how to protect it.  Is is the
    process of examining all of your risks, and ranking those risks by
    level of severity.  This process involves making cost-effective

Site Security Policy Handbook Working Group [Page 10] RFC 1244 Site Security Handbook July 1991

    decisions on what you want to protect.  The old security adage
    says that you should not spend more to protect something than it
    is actually worth.
    A full treatment of risk analysis is outside the scope of this
    document.  [3, FITES] and [16, PFLEEGER] provide introductions to
    this topic.  However, there are two elements of a risk analysis
    that will be briefly covered in the next two sections:
       1. Identifying the assets
       2. Identifying the threats
    For each asset, the basic goals of security are availability,
    confidentiality, and integrity.  Each threat should be examined
    with an eye to how the threat could affect these areas.
 2.2.2  Identifying the Assets
    One step in a risk analysis is to identify all the things that
    need to be protected.  Some things are obvious, like all the
    various pieces of hardware, but some are overlooked, such as the
    people who actually use the systems. The essential point is to
    list all things that could be affected by a security problem.
    One list of categories is suggested by Pfleeger [16, PFLEEGER,
    page 459]; this list is adapted from that source:
       1. Hardware: cpus, boards, keyboards, terminals,
          workstations, personal computers, printers, disk
          drives, communication lines, terminal servers, routers.
       2. Software: source programs, object programs,
          utilities, diagnostic programs, operating systems,
          communication programs.
       3. Data: during execution, stored on-line, archived off-line,
          backups, audit logs, databases, in transit over
          communication media.
       4. People: users, people needed to run systems.
       5. Documentation: on programs, hardware, systems, local
          administrative procedures.
       6. Supplies: paper, forms, ribbons, magnetic media.

Site Security Policy Handbook Working Group [Page 11] RFC 1244 Site Security Handbook July 1991

 2.2.3  Identifying the Threats
    Once the assets requiring protection are identified, it is
    necessary to identify threats to those assests.  The threats can
    then be examined to determine what potential for loss exists.  It
    helps to consider from what threats you are trying to protect your
    The following sections describe a few of the possible threats.  Unauthorized Access
       A common threat that concerns many sites is unauthorized access
       to computing facilities.  Unauthorized access takes many forms.
       One means of unauthorized access is the use of another user's
       account to gain access to a system.  The use of any computer
       resource without prior permission may be considered
       unauthorized access to computing facilities.
       The seriousness of an unauthorized access will vary from site
       to site.  For some sites, the mere act of granting access to an
       unauthorized user may cause irreparable harm by negative media
       coverage.  For other sites, an unauthorized access opens the
       door to other security threats.  In addition, some sites may be
       more frequent targets than others; hence the risk from
       unauthorized access will vary from site to site.  The Computer
       Emergency Response Team (CERT - see section has
       observed that well-known universities, government sites, and
       military sites seem to attract more intruders.  Disclosure of Information
       Another common threat is disclosure of information.  Determine
       the value or sensitivity of the information stored on your
       computers.  Disclosure of a password file might allow for
       future unauthorized accesses.  A glimpse of a proposal may give
       a competitor an unfair advantage.  A technical paper may
       contain years of valuable research.  Denial of Service
       Computers and networks provide valuable services to their
       users.  Many people rely on these services in order to perform
       their jobs efficiently.  When these services are not available
       when called upon, a loss in productivity results.
       Denial of service comes in many forms and might affect users in
       a number of ways.  A network may be rendered unusable by a

Site Security Policy Handbook Working Group [Page 12] RFC 1244 Site Security Handbook July 1991

       rogue packet, jamming, or by a disabled network component.  A
       virus might slow down or cripple a computer system.  Each site
       should determine which services are essential, and for each of
       these services determine the affect to the site if that service
       were to become disabled.

2.3 Policy Issues

 There are a number of issues that must be addressed when developing a
 security policy.  These are:
    1.  Who is allowed to use the resources?
    2.  What is the proper use of the resources?
    3.  Who is authorized to grant access and approve usage?
    4.  Who may have system administration privileges?
    5.  What are the user's rights and responsibilities?
    6.  What are the rights and responsibilities of the
        system administrator vs. those of the user?
    7.  What do you do with sensitive information?
 These issues will be discussed below.  In addition you may wish to
 include a section in your policy concerning ethical use of computing
 resources.  Parker, Swope and Baker [17, PARKER90] and Forester and
 Morrison [18, FORESTER] are two useful references that address
 ethical issues.
 2.3.1  Who is Allowed to use the Resources?
    One step you must take in developing your security policy is
    defining who is allowed to use your system and services.  The
    policy should explicitly state who is authorized to use what
 2.3.2  What is the Proper Use of the Resources?
    After determining who is allowed access to system resources it is
    necessary to provide guidelines for the acceptable use of the
    resources.  You may have different guidelines for different types
    of users (i.e., students, faculty, external users).  The policy
    should state what is acceptable use as well as unacceptable use.
    It should also include types of use that may be restricted.
    Define limits to access and authority.  You will need to consider
    the level of access various users will have and what resources
    will be available or restricted to various groups of people.
    Your acceptable use policy should clearly state that individual
    users are responsible for their actions.  Their responsibility

Site Security Policy Handbook Working Group [Page 13] RFC 1244 Site Security Handbook July 1991

    exists regardless of the security mechanisms that are in place.
    It should be clearly stated that breaking into accounts or
    bypassing security is not permitted.
    The following points should be covered when developing an
    acceptable use policy:
       o Is breaking into accounts permitted?
       o Is cracking passwords permitted?
       o Is disrupting service permitted?
       o Should users assume that a file being world-readable
         grants them the authorization to read it?
       o Should users be permitted to modify files that are
         not their own even if they happen to have write
       o Should users share accounts?
    The answer to most of these questions will be "no".
    You may wish to incorporate a statement in your policies
    concerning copyrighted and licensed software.  Licensing
    agreements with vendors may require some sort of effort on your
    part to ensure that the license is not violated.  In addition, you
    may wish to inform users that the copying of copyrighted software
    may be a violation of the copyright laws, and is not permitted.
    Specifically concerning copyrighted and/or licensed software, you
    may wish to include the following information:
       o Copyrighted and licensed software may not be duplicated
         unless it is explicitly stated that you may do so.
       o Methods of conveying information on the
         copyright/licensed status of software.
       o When in doubt, DON'T COPY.
    Your acceptable use policy is very important.  A policy which does
    not clearly state what is not permitted may leave you unable to
    prove that a user violated policy.
    There are exception cases like tiger teams and users or
    administrators wishing for "licenses to hack" -- you may face the
    situation where users will want to "hack" on your services for
    security research purposes.  You should develop a policy that will
    determine whether you will permit this type of research on your
    services and if so, what your guidelines for such research will
    Points you may wish to cover in this area:

Site Security Policy Handbook Working Group [Page 14] RFC 1244 Site Security Handbook July 1991

       o Whether it is permitted at all.
       o What type of activity is permitted: breaking in, releasing
         worms, releasing viruses, etc..
       o What type of controls must be in place to ensure that it
         does not get out of control (e.g., separate a segment of
         your network for these tests).
       o How you will protect other users from being victims of
         these activities, including external users and networks.
       o The process for obtaining permission to conduct these
    In cases where you do permit these activities, you should isolate
    the portions of the network that are being tested from your main
    network.  Worms and viruses should never be released on a live
    You may also wish to employ, contract, or otherwise solicit one or
    more people or organizations to evaluate the security of your
    services, of which may include "hacking".  You may wish to provide
    for this in your policy.
 2.3.3  Who Is Authorized to Grant Access and Approve Usage?
    Your policy should state who is authorized to grant access to your
    services.  Further, it must be determined what type of access they
    are permitted to give.  If you do not have control over who is
    granted access to your system, you will not have control over who
    is using your system.  Controlling who has the authorization to
    grant access will also enable you to know who was or was not
    granting access if problems develop later.
    There are many schemes that can be developed to control the
    distribution of access to your services.  The following are the
    factors that you must consider when determining who will
    distribute access to your services:
       o Will you be distributing access from a centralized
         point or at various points?
    You can have a centralized distribution point to a distributed
    system where various sites or departments independently authorize
    access.  The trade off is between security and convenience.  The
    more centralized, the easier to secure.
       o What methods will you use for creating accounts and
         terminating access?
    From a security standpoint, you need to examine the mechanism that

Site Security Policy Handbook Working Group [Page 15] RFC 1244 Site Security Handbook July 1991

    you will be using to create accounts.  In the least restrictive
    case, the people who are authorized to grant access would be able
    to go into the system directly and create an account by hand or
    through vendor supplied mechanisms.  Generally, these mechanisms
    place a great deal of trust in the person running them, and the
    person running them usually has a large amount of privileges.  If
    this is the choice you make, you need to select someone who is
    trustworthy to perform this task.  The opposite solution is to
    have an integrated system that the people authorized to create
    accounts run, or the users themselves may actually run.  Be aware
    that even in the restrictive case of having a mechanized facility
    to create accounts does not remove the potential for abuse.
    You should have specific procedures developed for the creation of
    accounts.  These procedures should be well documented to prevent
    confusion and reduce mistakes.  A security vulnerability in the
    account authorization process is not only possible through abuse,
    but is also possible if a mistake is made.  Having clear and well
    documented procedure will help ensure that these mistakes won't
    happen.  You should also be sure that the people who will be
    following these procedures understand them.
    The granting of access to users is one of the most vulnerable of
    times.  You should ensure that the selection of an initial
    password cannot be easily guessed.  You should avoid using an
    initial password that is a function of the username, is part of
    the user's name, or some algorithmically generated password that
    can easily be guessed.  In addition, you should not permit users
    to continue to use the initial password indefinitely.  If
    possible, you should force users to change the initial password
    the first time they login.  Consider that some users may never
    even login, leaving their password vulnerable indefinitely.  Some
    sites choose to disable accounts that have never been accessed,
    and force the owner to reauthorize opening the account.
 2.3.4  Who May Have System Administration Privileges?
    One security decision that needs to be made very carefully is who
    will have access to system administrator privileges and passwords
    for your services.  Obviously, the system administrators will need
    access, but inevitably other users will request special
    privileges.  The policy should address this issue.  Restricting
    privileges is one way to deal with threats from local users.  The
    challenge is to balance restricting access to these to protect
    security with giving people who need these privileges access so
    that they can perform their tasks.  One approach that can be taken
    is to grant only enough privilege to accomplish the necessary

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    Additionally, people holding special privileges should be
    accountable to some authority and this should also be identified
    within the site's security policy.  If the people you grant
    privileges to are not accountable, you run the risk of losing
    control of your system and will have difficulty managing a
    compromise in security.
 2.3.5  What Are The Users' Rights and Responsibilities?
    The policy should incorporate a statement on the users' rights and
    responsibilities concerning the use of the site's computer systems
    and services.  It should be clearly stated that users are
    responsible for understanding and respecting the security rules of
    the systems they are using.  The following is a list of topics
    that you may wish to cover in this area of the policy:
       o What guidelines you have regarding resource consumption
         (whether users are restricted, and if so, what the
         restrictions are).
       o What might constitute abuse in terms of system performance.
       o Whether users are permitted to share accounts or let others
         use their accounts.
       o How "secret" users should keep their passwords.
       o How often users should change their passwords and any other
         password restrictions or requirements.
       o Whether you provide backups or expect the users to create
         their own.
       o Disclosure of information that may be proprietary.
       o Statement on Electronic Mail Privacy (Electronic
         Communications Privacy Act).
       o Your policy concerning controversial mail or postings to
         mailing lists or discussion groups (obscenity, harassment,
       o Policy on electronic communications: mail forging, etc.
    The Electronic Mail Association sponsored a white paper on the
    privacy of electronic mail in companies [4].  Their basic
    recommendation is that every site should have a policy on the
    protection of employee privacy.  They also recommend that
    organizations establish privacy policies that deal with all media,
    rather than singling out electronic mail.
    They suggest five criteria for evaluating any policy:
       1. Does the policy comply with law and with duties to
          third parties?
       2. Does the policy unnecessarily compromise the interest of

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          the employee, the employer or third parties?
       3. Is the policy workable as a practical matter and likely to
          be enforced?
       4. Does the policy deal appropriately with all different
          forms of communications and record keeping with the office?
       5. Has the policy been announced in advance and agreed to by
          all concerned?
 2.3.6  What Are The Rights and Responsibilities of System
        Administrators Versus Rights of Users
    There is a tradeoff between a user's right to absolute privacy and
    the need of system administrators to gather sufficient information
    to diagnose problems.  There is also a distinction between a
    system administrator's need to gather information to diagnose
    problems and investigating security violations.  The policy should
    specify to what degree system administrators can examine user
    files to diagnose problems or for other purposes, and what rights
    you grant to the users.  You may also wish to make a statement
    concerning system administrators' obligation to maintaining the
    privacy of information viewed under these circumstances.  A few
    questions that should be answered are:
       o Can an administrator monitor or read a user's files
         for any reason?
       o What are the liabilities?
       o Do network administrators have the right to examine
         network or host traffic?
 2.3.7  What To Do With Sensitive Information
    Before granting users access to your services, you need to
    determine at what level you will provide for the security of data
    on your systems.  By determining this, you are determining the
    level of sensitivity of data that users should store on your
    systems.  You do not want users to store very sensitive
    information on a system that you are not going to secure very
    well.  You need to tell users who might store sensitive
    information what services, if any, are appropriate for the storage
    of sensitive information.  This part should include storing of
    data in different ways (disk, magnetic tape, file servers, etc.).
    Your policy in this area needs to be coordinated with the policy
    concerning the rights of system administrators versus users (see
    section 2.3.6).

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2.4 What Happens When the Policy is Violated

 It is obvious that when any type of official policy is defined, be it
 related to computer security or not, it will eventually be broken.
 The violation may occur due to an individual's negligence, accidental
 mistake, having not been properly informed of the current policy, or
 not understanding the current policy.  It is equally possible that an
 individual (or group of individuals) may knowingly perform an act
 that is in direct violation of the defined policy.
 When a policy violation has been detected, the immediate course of
 action should be pre-defined to ensure prompt and proper enforcement.
 An investigation should be performed to determine how and why the
 violation occurred.  Then the appropriate corrective action should be
 executed.  The type and severity of action taken varies depending on
 the type of violation that occurred.
 2.4.1  Determining the Response to Policy Violations
    Violations to policy may be committed by a wide variety of users.
    Some may be local users and others may be from outside the local
    environment.  Sites may find it helpful to define what it
    considers "insiders" and "outsiders" based upon administrative,
    legal or political boundaries.  These boundaries imply what type
    of action must be taken to correct the offending party; from a
    written reprimand to pressing legal charges.  So, not only do you
    need to define actions based on the type of violation, you also
    need to have a clearly defined series of actions based on the kind
    of user violating your computer security policy.  This all seems
    rather complicated, but should be addressed long before it becomes
    necessary as the result of a violation.
    One point to remember about your policy is that proper education
    is your best defense.  For the outsiders who are using your
    computer legally, it is your responsibility to verify that these
    individuals are aware of the policies that you have set forth.
    Having this proof may assist you in the future if legal action
    becomes necessary.
    As for users who are using your computer illegally, the problem is
    basically the same.  What type of user violated the policy and how
    and why did they do it?  Depending on the results of your
    investigation, you may just prefer to "plug" the hole in your
    computer security and chalk it up to experience.  Or if a
    significant amount of loss was incurred, you may wish to take more
    drastic action.

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 2.4.2  What to do When Local Users Violate the Policy of a Remote
    In the event that a local user violates the security policy of a
    remote site, the local site should have a clearly defined set of
    administrative actions to take concerning that local user.  The
    site should also be prepared to protect itself against possible
    actions by the remote site.  These situations involve legal issues
    which should be addressed when forming the security policy.
 2.4.3  Defining Contacts and Responsibilities to Outside
    The local security policy should include procedures for
    interaction with outside organizations.  These include law
    enforcement agencies, other sites, external response team
    organizations (e.g., the CERT, CIAC) and various press agencies.
    The procedure should state who is authorized to make such contact
    and how it should be handled.  Some questions to be answered
       o Who may talk to the press?
       o When do you contact law enforcement and investigative agencies?
       o If a connection is made from a remote site, is the
         system manager authorized to contact that site?
       o Can data be released?  What kind?
    Detailed contact information should be readily available along
    with clearly defined procedures to follow.
 2.4.4  What are the Responsibilities to our Neighbors and Other
        Internet Sites?
    The Security Policy Working Group within the IETF is working on a
    document entitled, "Policy Guidelines for the Secure Operation of
    the Internet" [23].  It addresses the issue that the Internet is a
    cooperative venture and that sites are expected to provide mutual
    security assistance.  This should be addressed when developing a
    site's policy.  The major issue to be determined is how much
    information should be released.  This will vary from site to site
    according to the type of site (e.g., military, education,
    commercial) as well as the type of security violation that
 2.4.5  Issues for Incident Handling Procedures
    Along with statements of policy, the document being prepared
    should include procedures for incident handling.  This is covered

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    in detail in the next chapter.  There should be procedures
    available that cover all facets of policy violation.

2.5 Locking In or Out

 Whenever a site suffers an incident which may compromise computer
 security, the strategies for reacting may be influenced by two
 opposing pressures.
 If management fears that the site is sufficiently vulnerable, it may
 choose a "Protect and Proceed" strategy.  This approach will have as
 its primary goal the protection and preservation of the site
 facilities and to provide for normalcy for its users as quickly as
 possible.  Attempts will be made to actively interfere with the
 intruder's processes, prevent further access and begin immediate
 damage assessment and recovery.  This process may involve shutting
 down the facilities, closing off access to the network, or other
 drastic measures.  The drawback is that unless the intruder is
 identified directly, they may come back into the site via a different
 path, or may attack another site.
 The alternate approach, "Pursue and Prosecute", adopts the opposite
 philosophy and goals.  The primary goal is to allow intruders to
 continue their activities at the site until the site can identify the
 responsible persons.  This approach is endorsed by law enforcement
 agencies and prosecutors.  The drawback is that the agencies cannot
 exempt a site from possible user lawsuits if damage is done to their
 systems and data.
 Prosecution is not the only outcome possible if the intruder is
 identified.  If the culprit is an employee or a student, the
 organization may choose to take disciplinary actions.  The computer
 security policy needs to spell out the choices and how they will be
 selected if an intruder is caught.
 Careful consideration must be made by site management regarding their
 approach to this issue before the problem occurs.  The strategy
 adopted might depend upon each circumstance.  Or there may be a
 global policy which mandates one approach in all circumstances.  The
 pros and cons must be examined thoroughly and the users of the
 facilities must be made aware of the policy so that they understand
 their vulnerabilities no matter which approach is taken.
 The following are checklists to help a site determine which strategy
 to adopt: "Protect and Proceed" or "Pursue and Prosecute".

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 Protect and Proceed
    1. If assets are not well protected.
    2. If continued penetration could result in great
       financial risk.
    3. If the possibility or willingness to prosecute
       is not present.
    4. If user base is unknown.
    5. If users are unsophisticated and their work is
    6. If the site is vulnerable to lawsuits from users, e.g.,
       if their resources are undermined.
 Pursue and Prosecute
    1. If assets and systems are well protected.
    2. If good backups are available.
    3. If the risk to the assets is outweighed by the
       disruption caused by the present and possibly future
    4. If this is a concentrated attack occurring with great
       frequency and intensity.
    5. If the site has a natural attraction to intruders, and
       consequently regularly attracts intruders.
    6. If the site is willing to incur the financial (or other)
       risk to assets by allowing the penetrator continue.
    7. If intruder access can be controlled.
    8. If the monitoring tools are sufficiently well-developed
       to make the pursuit worthwhile.
    9. If the support staff is sufficiently clever and knowledgable
       about the operating system, related utilities, and systems
       to make the pursuit worthwhile.
    10. If there is willingness on the part of management to

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    11. If the system adminitrators know in general what kind of
        evidence would lead to prosecution.
    12. If there is established contact with knowledgeable law
    13. If there is a site representative versed in the relevant
        legal issues.
    14. If the site is prepared for possible legal action from
        its own users if their data or systems become compromised
        during the pursuit.

2.6 Interpreting the Policy

 It is important to define who will interpret the policy.  This could
 be an individual or a committee.  No matter how well written, the
 policy will require interpretation from time to time and this body
 would serve to review, interpret, and revise the policy as needed.

2.7 Publicizing the Policy

 Once the site security policy has been written and established, a
 vigorous process should be engaged to ensure that the policy
 statement is widely and thoroughly disseminated and discussed.  A
 mailing of the policy should not be considered sufficient.  A period
 for comments should be allowed before the policy becomes effective to
 ensure that all affected users have a chance to state their reactions
 and discuss any unforeseen ramifications.  Ideally, the policy should
 strike a balance between protection and productivity.
 Meetings should be held to elicit these comments, and also to ensure
 that the policy is correctly understood.  (Policy promulgators are
 not necessarily noted for their skill with the language.)  These
 meetings should involve higher management as well as line employees.
 Security is a collective effort.
 In addition to the initial efforts to publicize the policy, it is
 essential for the site to maintain a continual awareness of its
 computer security policy.  Current users may need periodic reminders
 New users should have the policy included as part of their site
 introduction packet.  As a condition for using the site facilities,
 it may be advisable to have them sign a statement that they have read
 and understood the policy.  Should any of these users require legal
 action for serious policy violations, this signed statement might
 prove to be a valuable aid.

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3. Establishing Procedures to Prevent Security Problems

 The security policy defines what needs to be protected.  This section
 discusses security procedures which specify what steps will be used
 to carry out the security policy.

3.1 Security Policy Defines What Needs to be Protected

 The security policy defines the WHAT's: what needs to be protected,
 what is most important, what the priorities are, and what the general
 approach to dealing with security problems should be.
 The security policy by itself doesn't say HOW things are protected.
 That is the role of security procedures, which this section
 discusses.  The security policy should be a high level document,
 giving general strategy.  The security procedures need to set out, in
 detail, the precise steps your site will take to protect itself.
 The security policy should include a general risk assessment of the
 types of threats a site is mostly likely to face and the consequences
 of those threats (see section 2.2).  Part of doing a risk assessment
 will include creating a general list of assets that should be
 protected (section 2.2.2).  This information is critical in devising
 cost-effective procedures.
 It is often tempting to start creating security procedures by
 deciding on different mechanisms first: "our site should have logging
 on all hosts, call-back modems, and smart cards for all users."  This
 approach could lead to some areas that have too much protection for
 the risk they face, and other areas that aren't protected enough.
 Starting with the security policy and the risks it outlines should
 ensure that the procedures provide the right level of protect for all

3.2 Identifing Possible Problems

 To determine risk, vulnerabilities must be identified.  Part of the
 purpose of the policy is to aid in shoring up the vulnerabilities and
 thus to decrease the risk in as many areas as possible.  Several of
 the more popular problem areas are presented in sections below.  This
 list is by no means complete.  In addition, each site is likely to
 have a few unique vulnerabilities.
 3.2.1  Access Points
    Access points are typically used for entry by unauthorized users.
    Having many access points increases the risk of access to an
    organization's computer and network facilities.

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    Network links to networks outside the organization allow access
    into the organization for all others connected to that external
    network.  A network link typically provides access to a large
    number of network services, and each service has a potential to be
    Dialup lines, depending on their configuration, may provide access
    merely to a login port of a single system.  If connected to a
    terminal server, the dialup line may give access to the entire
    Terminal servers themselves can be a source of problem.  Many
    terminal servers do not require any kind of authentication.
    Intruders often use terminal servers to disguise their actions,
    dialing in on a local phone and then using the terminal server to
    go out to the local network.  Some terminal servers are configured
    so that intruders can TELNET [19] in from outside the network, and
    then TELNET back out again, again serving to make it difficult to
    trace them.
 3.2.2  Misconfigured Systems
    Misconfigured systems form a large percentage of security holes.
    Today's operating systems and their associated software have
    become so complex that understanding how the system works has
    become a full-time job.  Often, systems managers will be non-
    specialists chosen from the current organization's staff.
    Vendors are also partly responsible for misconfigured systems. To
    make the system installation process easier, vendors occasionally
    choose initial configurations that are not secure in all
 3.2.3  Software Bugs
    Software will never be bug free.  Publicly known security bugs are
    common methods of unauthorized entry.  Part of the solution to
    this problem is to be aware of the security problems and to update
    the software when problems are detected.  When bugs are found,
    they should be reported to the vendor so that a solution to the
    problem can be implemented and distributed.
 3.2.4  "Insider" Threats
    An insider to the organization may be a considerable threat to the
    security of the computer systems.  Insiders often have direct
    access to the computer and network hardware components.  The
    ability to access the components of a system makes most systems

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    easier to compromise.  Most desktop workstations can be easily
    manipulated so that they grant privileged access.  Access to a
    local area network provides the ability to view possibly sensitive
    data traversing the network.

3.3 Choose Controls to Protect Assets in a Cost-Effective Way

 After establishing what is to be protected, and assessing the risks
 these assets face, it is necessary to decide how to implement the
 controls which protect these assets.  The controls and protection
 mechanisms should be selected in a way so as to adequately counter
 the threats found during risk assessment, and to implement those
 controls in a cost effective manner.  It makes little sense to spend
 an exorbitant sum of money and overly constrict the user base if the
 risk of exposure is very small.
 3.3.1  Choose the Right Set of Controls
    The controls that are selected represent the physical embodiment
    of your security policy.  They are the first and primary line of
    defense in the protection of your assets.  It is therefore most
    important to ensure that the controls that you select are the
    right set of controls.  If the major threat to your system is
    outside penetrators, it probably doesn't make much sense to use
    biometric devices to authenticate your regular system users.  On
    the other hand, if the major threat is unauthorized use of
    computing resources by regular system users, you'll probably want
    to establish very rigorous automated accounting procedures.
 3.3.2  Use Common Sense
    Common sense is the most appropriate tool that can be used to
    establish your security policy.  Elaborate security schemes and
    mechanisms are impressive, and they do have their place, yet there
    is little point in investing money and time on an elaborate
    implementation scheme if the simple controls are forgotten.  For
    example, no matter how elaborate a system you put into place on
    top of existing security controls, a single user with a poor
    password can still leave your system open to attack.

3.4 Use Multiple Strategies to Protect Assets

 Another method of protecting assets is to use multiple strategies.
 In this way, if one strategy fails or is circumvented, another
 strategy comes into play to continue protecting the asset.  By using
 several simpler strategies, a system can often be made more secure
 than if one very sophisticated method were used in its place.  For
 example, dial-back modems can be used in conjunction with traditional

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 logon mechanisms.  Many similar approaches could be devised that
 provide several levels of protection for assets.  However, it's very
 easy to go overboard with extra mechanisms.  One must keep in mind
 exactly what it is that needs to be protected.

3.5 Physical Security

 It is a given in computer security if the system itself is not
 physically secure, nothing else about the system can be considered
 secure.  With physical access to a machine, an intruder can halt the
 machine, bring it back up in privileged mode, replace or alter the
 disk, plant Trojan horse programs (see section, or take any
 number of other undesirable (and hard to prevent) actions.
 Critical communications links, important servers, and other key
 machines should be located in physically secure areas.  Some security
 systems (such as Kerberos) require that the machine be physically
 If you cannot physically secure machines, care should be taken about
 trusting those machines.  Sites should consider limiting access from
 non-secure machines to more secure machines.  In particular, allowing
 trusted access (e.g., the BSD Unix remote commands such as rsh) from
 these kinds of hosts is particularly risky.
 For machines that seem or are intended to be physically secure, care
 should be taken about who has access to the machines.  Remember that
 custodial and maintenance staff often have keys to rooms.

3.6 Procedures to Recognize Unauthorized Activity

 Several simple procedures can be used to detect most unauthorized
 uses of a computer system.  These procedures use tools provided with
 the operating system by the vendor, or tools publicly available from
 other sources.
 3.6.1  Monitoring System Use
    System monitoring can be done either by a system administrator, or
    by software written for the purpose.  Monitoring a system involves
    looking at several parts of the system and searching for anything
    unusual.  Some of the easier ways to do this are described in this
    The most important thing about monitoring system use is that it be
    done on a regular basis.  Picking one day out of the month to
    monitor the system is pointless, since a security breach can be
    isolated to a matter of hours.  Only by maintaining a constant

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    vigil can you expect to detect security violations in time to
    react to them.
 3.6.2  Tools for Monitoring the System
    This section describes tools and methods for monitoring a system
    against unauthorized access and use.  Logging
       Most operating systems store numerous bits of information in
       log files.  Examination of these log files on a regular basis
       is often the first line of defense in detecting unauthorized
       use of the system.
  1. Compare lists of currently logged in users and past

login histories. Most users typically log in and out

            at roughly the same time each day.  An account logged
            in outside the "normal" time for the account may be in
            use by an intruder.
  1. Many systems maintain accounting records for billing

purposes. These records can also be used to determine

            usage patterns for the system; unusual accounting records
            may indicate unauthorized use of the system.
  1. System logging facilities, such as the UNIX "syslog"

utility, should be checked for unusual error messages

            from system software.  For example, a large number of
            failed login attempts in a short period of time may
            indicate someone trying to guess passwords.
  1. Operating system commands which list currently executing

processes can be used to detect users running programs

            they are not authorized to use, as well as to detect
            unauthorized programs which have been started by an
            intruder.  Monitoring Software
       Other monitoring tools can easily be constructed using standard
       operating system software, by using several, often unrelated,
       programs together.  For example, checklists of file ownerships
       and permission settings can be constructed (for example, with
       "ls" and "find" on UNIX) and stored off-line.  These lists can
       then be reconstructed periodically and compared against the
       master checklist (on UNIX, by using the "diff" utility).
       Differences may indicate that unauthorized modifications have

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       been made to the system.
       Still other tools are available from third-party vendors and
       public software distribution sites.  Section 3.9.9 lists
       several sources from which you can learn what tools are
       available and how to get them.  Other Tools
       Other tools can also be used to monitor systems for security
       violations, although this is not their primary purpose.  For
       example, network monitors can be used to detect and log
       connections from unknown sites.
 3.6.3  Vary the Monitoring Schedule
    The task of system monitoring is not as daunting as it may seem.
    System administrators can execute many of the commands used for
    monitoring periodically throughout the day during idle moments
    (e.g., while talking on the telephone), rather than spending fixed
    periods of each day monitoring the system.  By executing the
    commands frequently, you will rapidly become used to seeing
    "normal" output, and will easily spot things which are out of the
    ordinary.  In addition, by running various monitoring commands at
    different times throughout the day, you make it hard for an
    intruder to predict your actions.  For example, if an intruder
    knows that each day at 5:00 p.m. the system is checked to see that
    everyone has logged off, he will simply wait until after the check
    has completed before logging in.  But the intruder cannot guess
    when a system administrator might type a command to display all
    logged-in users, and thus he runs a much greater risk of
    Despite the advantages that regular system monitoring provides,
    some intruders will be aware of the standard logging mechanisms in
    use on systems they are attacking.  They will actively pursue and
    attempt to disable monitoring mechanisms.  Regular monitoring
    therefore is useful in detecting intruders, but does not provide
    any guarantee that your system is secure, nor should monitoring be
    considered an infallible method of detecting unauthorized use.

3.7 Define Actions to Take When Unauthorized Activity is Suspected

    Sections 2.4 and 2.5 discussed the course of action a site should
    take when it suspects its systems are being abused.  The computer
    security policy should state the general approach towards dealing
    with these problems.

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    The procedures for dealing with these types of problems should be
    written down.  Who has authority to decide what actions will be
    taken?  Should law enforcement be involved?  Should your
    organization cooperate with other sites in trying to track down an
    intruder?  Answers to all the questions in section 2.4 should be
    part of the incident handling procedures.
    Whether you decide to lock out or pursue intruders, you should
    have tools and procedures ready to apply.  It is best to work up
    these tools and procedures before you need them.  Don't wait until
    an intruder is on your system to figure out how to track the
    intruder's actions; you will be busy enough if an intruder

3.8 Communicating Security Policy

 Security policies, in order to be effective, must be communicated to
 both the users of the system and the system maintainers.  This
 section describes what these people should be told, and how to tell
 3.8.1  Educating the Users
    Users should be made aware of how the computer systems are
    expected to be used, and how to protect themselves from
    unauthorized users.  Proper Account/Workstation Use
       All users should be informed about what is considered the
       "proper" use of their account or workstation ("proper" use is
       discussed in section 2.3.2).  This can most easily be done at
       the time a user receives their account, by giving them a policy
       statement.  Proper use policies typically dictate things such
       as whether or not the account or workstation may be used for
       personal activities (such as checkbook balancing or letter
       writing), whether profit-making activities are allowed, whether
       game playing is permitted, and so on.  These policy statements
       may also be used to summarize how the computer facility is
       licensed and what software licenses are held by the
       institution; for example, many universities have educational
       licenses which explicitly prohibit commercial uses of the
       system.  A more complete list of items to consider when writing
       a policy statement is given in section 2.3.  Account/Workstation Management Procedures
       Each user should be told how to properly manage their account

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       and workstation.  This includes explaining how to protect files
       stored on the system, how to log out or lock the terminal or
       workstation, and so on.  Much of this information is typically
       covered in the "beginning user" documentation provided by the
       operating system vendor, although many sites elect to
       supplement this material with local information.
       If your site offers dial-up modem access to the computer
       systems, special care must be taken to inform users of the
       security problems inherent in providing this access.  Issues
       such as making sure to log out before hanging up the modem
       should be covered when the user is initially given dial-up
       Likewise, access to the systems via local and wide-area
       networks presents its own set of security problems which users
       should be made aware of.  Files which grant "trusted host" or
       "trusted user" status to remote systems and users should be
       carefully explained.  Determining Account Misuse
       Users should be told how to detect unauthorized access to their
       account.  If the system prints the last login time when a user
       logs in, he or she should be told to check that time and note
       whether or not it agrees with the last time he or she actually
       logged in.
       Command interpreters on some systems (e.g., the UNIX C shell)
       maintain histories of the last several commands executed.
       Users should check these histories to be sure someone has not
       executed other commands with their account.  Problem Reporting Procedures
       A procedure should be developed to enable users to report
       suspected misuse of their accounts or other misuse they may
       have noticed.  This can be done either by providing the name
       and telephone number of a system administrator who manages
       security of the computer system, or by creating an electronic
       mail address (e.g., "security") to which users can address
       their problems.
 3.8.2  Educating the Host Administrators
    In many organizations, computer systems are administered by a wide
    variety of people.  These administrators must know how to protect
    their own systems from attack and unauthorized use, as well as how

Site Security Policy Handbook Working Group [Page 31] RFC 1244 Site Security Handbook July 1991

    to communicate successful penetration of their systems to other
    administrators as a warning.  Account Management Procedures
       Care must be taken when installing accounts on the system in
       order to make them secure.  When installing a system from
       distribution media, the password file should be examined for
       "standard" accounts provided by the vendor.  Many vendors
       provide accounts for use by system services or field service
       personnel.  These accounts typically have either no password or
       one which is common knowledge.  These accounts should be given
       new passwords if they are needed, or disabled or deleted from
       the system if they are not.
       Accounts without passwords are generally very dangerous since
       they allow anyone to access the system.  Even accounts which do
       not execute a command interpreter (e.g., accounts which exist
       only to see who is logged in to the system) can be compromised
       if set up incorrectly.  A related concept, that of "anonymous"
       file transfer (FTP) [20], allows users from all over the
       network to access your system to retrieve files from (usually)
       a protected disk area.  You should carefully weigh the benefits
       that an account without a password provides against the
       security risks of providing such access to your system.
       If the operating system provides a "shadow" password facility
       which stores passwords in a separate file accessible only to
       privileged users, this facility should be used.  System V UNIX,
       SunOS 4.0 and above, and versions of Berkeley UNIX after 4.3BSD
       Tahoe, as well as others, provide this feature.  It protects
       passwords by hiding their encrypted values from unprivileged
       users.  This prevents an attacker from copying your password
       file to his or her machine and then attempting to break the
       passwords at his or her leisure.
       Keep track of who has access to privileged user accounts (e.g.,
       "root" on UNIX or "MAINT" on VMS).  Whenever a privileged user
       leaves the organization or no longer has need of the privileged
       account, the passwords on all privileged accounts should be
       changed.  Configuration Management Procedures
       When installing a system from the distribution media or when
       installing third-party software, it is important to check the
       installation carefully.  Many installation procedures assume a
       "trusted" site, and hence will install files with world write

Site Security Policy Handbook Working Group [Page 32] RFC 1244 Site Security Handbook July 1991

       permission enabled, or otherwise compromise the security of
       Network services should also be examined carefully when first
       installed.  Many vendors provide default network permission
       files which imply that all outside hosts are to be "trusted",
       which is rarely the case when connected to wide-area networks
       such as the Internet.
       Many intruders collect information on the vulnerabilities of
       particular system versions.  The older a system, the more
       likely it is that there are security problems in that version
       which have since been fixed by the vendor in a later release.
       For this reason, it is important to weigh the risks of not
       upgrading to a new operating system release (thus leaving
       security holes unplugged) against the cost of upgrading to the
       new software (possibly breaking third-party software, etc.).
       Bug fixes from the vendor should be weighed in a similar
       fashion, with the added note that "security" fixes from a
       vendor usually address fairly serious security problems.
       Other bug fixes, received via network mailing lists and the
       like, should usually be installed, but not without careful
       examination.  Never install a bug fix unless you're sure you
       know what the consequences of the fix are - there's always the
       possibility that an intruder has suggested a "fix" which
       actually gives him or her access to your system.  Recovery Procedures - Backups
       It is impossible to overemphasize the need for a good backup
       strategy.  File system backups not only protect you in the
       event of hardware failure or accidental deletions, but they
       also protect you against unauthorized changes made by an
       intruder.  Without a copy of your data the way it's "supposed"
       to be, it can be difficult to undo something an attacker has
       Backups, especially if run daily, can also be useful in
       providing a history of an intruder's activities.  Looking
       through old backups can establish when your system was first
       penetrated.  Intruders may leave files around which, although
       deleted later, are captured on the backup tapes.  Backups can
       also be used to document an intruder's activities to law
       enforcement agencies if necessary.
       A good backup strategy will dump the entire system to tape at
       least once a month.  Partial (or "incremental") dumps should be

Site Security Policy Handbook Working Group [Page 33] RFC 1244 Site Security Handbook July 1991

       done at least twice a week, and ideally they should be done
       daily.  Commands specifically designed for performing file
       system backups (e.g., UNIX "dump" or VMS "BACKUP") should be
       used in preference to other file copying commands, since these
       tools are designed with the express intent of restoring a
       system to a known state.  Problem Reporting Procedures
       As with users, system administrators should have a defined
       procedure for reporting security problems.  In large
       installations, this is often done by creating an electronic
       mail alias which contains the names of all system
       administrators in the organization.  Other methods include
       setting up some sort of response team similar to the CERT, or
       establishing a "hotline" serviced by an existing support group.

3.9 Resources to Prevent Security Breaches

 This section discusses software, hardware, and procedural resources
 that can be used to support your site security policy.
 3.9.1  Network Connections and Firewalls
    A "firewall" is put in place in a building to provide a point of
    resistance to the entry of flames into another area.  Similarly, a
    secretary's desk and reception area provides a point of
    controlling access to other office spaces.  This same technique
    can be applied to a computer site, particularly as it pertains to
    network connections.
    Some sites will be connected only to other sites within the same
    organization and will not have the ability to connect to other
    networks.  Sites such as these are less susceptible to threats
    from outside their own organization, although intrusions may still
    occur via paths such as dial-up modems.  On the other hand, many
    other organizations will be connected to other sites via much
    larger networks, such as the Internet.  These sites are
    susceptible to the entire range of threats associated with a
    networked environment.
    The risks of connecting to outside networks must be weighed
    against the benefits.  It may be desirable to limit connection to
    outside networks to those hosts which do not store sensitive
    material, keeping "vital" machines (such as those which maintain
    company payroll or inventory systems) isolated.  If there is a
    need to participate in a Wide Area Network (WAN), consider
    restricting all access to your local network through a single

Site Security Policy Handbook Working Group [Page 34] RFC 1244 Site Security Handbook July 1991

    system.  That is, all access to or from your own local network
    must be made through a single host computer that acts as a
    firewall between you and the outside world.  This firewall system
    should be rigorously controlled and password protected, and
    external users accessing it should also be constrained by
    restricting the functionality available to remote users.  By using
    this approach, your site could relax some of the internal security
    controls on your local net, but still be afforded the protection
    of a rigorously controlled host front end.
    Note that even with a firewall system, compromise of the firewall
    could result in compromise of the network behind the firewall.
    Work has been done in some areas to construct a firewall which
    even when compromised, still protects the local network [6,
 3.9.2  Confidentiality
    Confidentiality, the act of keeping things hidden or secret, is
    one of the primary goals of computer security practitioners.
    Several mechanisms are provided by most modern operating systems
    to enable users to control the dissemination of information.
    Depending upon where you work, you may have a site where
    everything is protected, or a site where all information is
    usually regarded as public, or something in-between.  Most sites
    lean toward the in-between, at least until some penetration has
    Generally, there are three instances in which information is
    vulnerable to disclosure: when the information is stored on a
    computer system, when the information is in transit to another
    system (on the network), and when the information is stored on
    backup tapes.
    The first of these cases is controlled by file permissions, access
    control lists, and other similar mechanisms.  The last can be
    controlled by restricting access to the backup tapes (by locking
    them in a safe, for example).  All three cases can be helped by
    using encryption mechanisms.  Encryption (hardware and software)
       Encryption is the process of taking information that exists in
       some readable form and converting it into a non-readable form.
       There are several types of commercially available encryption
       packages in both hardware and software forms.  Hardware
       encryption engines have the advantage that they are much faster
       than the software equivalent, yet because they are faster, they

Site Security Policy Handbook Working Group [Page 35] RFC 1244 Site Security Handbook July 1991

       are of greater potential benefit to an attacker who wants to
       execute a brute-force attack on your encrypted information.
       The advantage of using encryption is that, even if other access
       control mechanisms (passwords, file permissions, etc.) are
       compromised by an intruder, the data is still unusable.
       Naturally, encryption keys and the like should be protected at
       least as well as account passwords.
       Information in transit (over a network) may be vulnerable to
       interception as well.  Several solutions to this exist, ranging
       from simply encrypting files before transferring them (end-to-
       end encryption) to special network hardware which encrypts
       everything it sends without user intervention (secure links).
       The Internet as a whole does not use secure links, thus end-
       to-end encryption must be used if encryption is desired across
       the Internet.  Data Encryption Standard (DES)
          DES is perhaps the most widely used data encryption
          mechanism today.  Many hardware and software implementations
          exist, and some commercial computers are provided with a
          software version.  DES transforms plain text information
          into encrypted data (or ciphertext) by means of a special
          algorithm and "seed" value called a key.  So long as the key
          is retained (or remembered) by the original user, the
          ciphertext can be restored to the original plain text.
          One of the pitfalls of all encryption systems is the need to
          remember the key under which a thing was encrypted (this is
          not unlike the password problem discussed elsewhere in this
          document).  If the key is written down, it becomes less
          secure.  If forgotten, there is little (if any) hope of
          recovering the original data.
          Most UNIX systems provide a DES command that enables a user
          to encrypt data using the DES algorithm.  Crypt
          Similar to the DES command, the UNIX "crypt" command allows
          a user to encrypt data.  Unfortunately, the algorithm used
          by "crypt" is very insecure (based on the World War II
          "Enigma" device), and files encrypted with this command can
          be decrypted easily in a matter of a few hours.  Generally,
          use of the "crypt" command should be avoided for any but the
          most trivial encryption tasks.

Site Security Policy Handbook Working Group [Page 36] RFC 1244 Site Security Handbook July 1991  Privacy Enhanced Mail
       Electronic mail normally transits the network in the clear
       (i.e., anyone can read it).  This is obviously not the optimal
       solution.  Privacy enhanced mail provides a means to
       automatically encrypt electronic mail messages so that a person
       eavesdropping at a mail distribution node is not (easily)
       capable of reading them.  Several privacy enhanced mail
       packages are currently being developed and deployed on the
       The Internet Activities Board Privacy Task Force has defined a
       draft standard, elective protocol for use in implementing
       privacy enhanced mail.  This protocol is defined in RFCs 1113,
       1114, and 1115 [7,8,9].  Please refer to the current edition of
       the "IAB Official Protocol Standards" (currently, RFC 1200
       [21]) for the standardization state and status of these
 3.9.3  Origin Authentication
    We mostly take it on faith that the header of an electronic mail
    message truly indicates the originator of a message.  However, it
    iseasy to "spoof", or forge the source of a mail message.  Origin
    authentication provides a means to be certain of the originator of
    a message or other object in the same way that a Notary Public
    assures a signature on a legal document.  This is done by means of
    a "Public Key" cryptosystem.
    A public key cryptosystem differs from a private key cryptosystem
    in several ways.  First, a public key system uses two keys, a
    Public Key that anyone can use (hence the name) and a Private Key
    that only the originator of a message uses.  The originator uses
    the private key to encrypt the message (as in DES).  The receiver,
    who has obtained the public key for the originator, may then
    decrypt the message.
    In this scheme, the public key is used to authenticate the
    originator's use of his or her private key, and hence the identity
    of the originator is more rigorously proven.  The most widely
    known implementation of a public key cryptosystem is the RSA
    system [26].  The Internet standard for privacy enhanced mail
    makes use of the RSA system.
 3.9.4  Information Integrity
    Information integrity refers to the state of information such that
    it is complete, correct, and unchanged from the last time in which

Site Security Policy Handbook Working Group [Page 37] RFC 1244 Site Security Handbook July 1991

    it was verified to be in an "integral" state.  The value of
    information integrity to a site will vary.  For example, it is
    more important for military and government installations to
    prevent the "disclosure" of classified information, whether it is
    right or wrong.  A bank, on the other hand, is far more concerned
    with whether the account information maintained for its customers
    is complete and accurate.
    Numerous computer system mechanisms, as well as procedural
    controls, have an influence on the integrity of system
    information.  Traditional access control mechanisms maintain
    controls over who can access system information.  These mechanisms
    alone are not sufficient in some cases to provide the degree of
    integrity required.  Some other mechanisms are briefly discussed
    It should be noted that there are other aspects to maintaining
    system integrity besides these mechanisms, such as two-person
    controls, and integrity validation procedures.  These are beyond
    the scope of this document.  Checksums
       Easily the simplest mechanism, a simple checksum routine can
       compute a value for a system file and compare it with the last
       known value.  If the two are equal, the file is probably
       unchanged.  If not, the file has been changed by some unknown
       Though it is the easiest to implement, the checksum scheme
       suffers from a serious failing in that it is not very
       sophisticated and a determined attacker could easily add enough
       characters to the file to eventually obtain the correct value.
       A specific type of checksum, called a CRC checksum, is
       considerably more robust than a simple checksum.  It is only
       slightly more difficult to implement and provides a better
       degree of catching errors.  It too, however, suffers from the
       possibility of compromise by an attacker.
       Checksums may be used to detect the altering of information.
       However, they do not actively guard against changes being made.
       For this, other mechanisms such as access controls and
       encryption should be used.

Site Security Policy Handbook Working Group [Page 38] RFC 1244 Site Security Handbook July 1991  Cryptographic Checksums
       Cryptographic checksums (also called cryptosealing) involve
       breaking a file up into smaller chunks, calculating a (CRC)
       checksum for each chunk, and adding the CRCs together.
       Depending upon the exact algorithm used, this can result in a
       nearly unbreakable method of determining whether a file has
       been changed.  This mechanism suffers from the fact that it is
       sometimes computationally intensive and may be prohibitive
       except in cases where the utmost integrity protection is
       Another related mechanism, called a one-way hash function (or a
       Manipulation Detection Code (MDC)) can also be used to uniquely
       identify a file.  The idea behind these functions is that no
       two inputs can produce the same output, thus a modified file
       will not have the same hash value.  One-way hash functions can
       be implemented efficiently on a wide variety of systems, making
       unbreakable integrity checks possible.  (Snefru, a one-way hash
       function available via USENET as well as the Internet is just
       one example of an efficient one-way hash function.) [10]
 3.9.5  Limiting Network Access
    The dominant network protocols in use on the Internet, IP (RFC
    791) [11], TCP (RFC 793) [12], and UDP (RFC 768) [13], carry
    certain control information which can be used to restrict access
    to certain hosts or networks within an organization.
    The IP packet header contains the network addresses of both the
    sender and recipient of the packet.  Further, the TCP and UDP
    protocols provide the notion of a "port", which identifies the
    endpoint (usually a network server) of a communications path.  In
    some instances, it may be desirable to deny access to a specific
    TCP or UDP port, or even to certain hosts and networks altogether.  Gateway Routing Tables
       One of the simplest approaches to preventing unwanted network
       connections is to simply remove certain networks from a
       gateway's routing tables.  This makes it "impossible" for a
       host to send packets to these networks.  (Most protocols
       require bidirectional packet flow even for unidirectional data
       flow, thus breaking one side of the route is usually
       This approach is commonly taken in "firewall" systems by
       preventing the firewall from advertising local routes to the

Site Security Policy Handbook Working Group [Page 39] RFC 1244 Site Security Handbook July 1991

       outside world.  The approach is deficient in that it often
       prevents "too much" (e.g., in order to prevent access to one
       system on the network, access to all systems on the network is
       disabled).  Router Packet Filtering
       Many commercially available gateway systems (more correctly
       called routers) provide the ability to filter packets based not
       only on sources or destinations, but also on source-destination
       combinations.  This mechanism can be used to deny access to a
       specific host, network, or subnet from any other host, network,
       or subnet.
       Gateway systems from some vendors (e.g., cisco Systems) support
       an even more complex scheme, allowing finer control over source
       and destination addresses.  Via the use of address masks, one
       can deny access to all but one host on a particular network.
       The cisco Systems also allow packet screening based on IP
       protocol type and TCP or UDP port numbers [14].
       This can also be circumvented by "source routing" packets
       destined for the "secret" network.  Source routed packets may
       be filtered out by gateways, but this may restrict other
       legitimate activities, such as diagnosing routing problems.
 3.9.6  Authentication Systems
    Authentication refers to the process of proving a claimed identity
    to the satisfaction of some permission-granting authority.
    Authentication systems are hardware, software, or procedural
    mechanisms that enable a user to obtain access to computing
    resources.  At the simplest level, the system administrator who
    adds new user accounts to the system is part of the system
    authentication mechanism.  At the other end of the spectrum,
    fingerprint readers or retinal scanners provide a very high-tech
    solution to establishing a potential user's identity.  Without
    establishing and proving a user's identity prior to establishing a
    session, your site's computers are vulnerable to any sort of
    Typically, a user authenticates himself or herself to the system
    by entering a password in response to a prompt.
    Challenge/Response mechanisms improve upon passwords by prompting
    the user for some piece of information shared by both the computer
    and the user (such as mother's maiden name, etc.).

Site Security Policy Handbook Working Group [Page 40] RFC 1244 Site Security Handbook July 1991  Kerberos
       Kerberos, named after the dog who in mythology is said to stand
       at the gates of Hades, is a collection of software used in a
       large network to establish a user's claimed identity.
       Developed at the Massachusetts Institute of Technology (MIT),
       it uses a combination of encryption and distributed databases
       so that a user at a campus facility can login and start a
       session from any computer located on the campus.  This has
       clear advantages in certain environments where there are a
       large number of potential users who may establish a connection
       from any one of a large number of workstations.  Some vendors
       are now incorporating Kerberos into their systems.
       It should be noted that while Kerberos makes several advances
       in the area of authentication, some security weaknesses in the
       protocol still remain [15].  Smart Cards
       Several systems use "smart cards" (a small calculator-like
       device) to help authenticate users.  These systems depend on
       the user having an object in their possession.  One such system
       involves a new password procedure that require a user to enter
       a value obtained from a "smart card" when asked for a password
       by the computer.  Typically, the host machine will give the
       user some piece of information that is entered into the
       keyboard of the smart card.  The smart card will display a
       response which must then be entered into the computer before
       the session will be established.  Another such system involves
       a smart card which displays a number which changes over time,
       but which is synchronized with the authentication software on
       the computer.
       This is a better way of dealing with authentication than with
       the traditional password approach.  On the other hand, some say
       it's inconvenient to carry the smart card.  Start-up costs are
       likely to be high as well.
 3.9.7  Books, Lists, and Informational Sources
    There are many good sources for information regarding computer
    security.  The annotated bibliography at the end of this document
    can provide you with a good start.  In addition, information can
    be obtained from a variety of other sources, some of which are
    described in this section.

Site Security Policy Handbook Working Group [Page 41] RFC 1244 Site Security Handbook July 1991  Security Mailing Lists
       The UNIX Security mailing list exists to notify system
       administrators of security problems before they become common
       knowledge, and to provide security enhancement information.  It
       is a restricted-access list, open only to people who can be
       verified as being principal systems people at a site.  Requests
       to join the list must be sent by either the site contact listed
       in the Defense Data Network's Network Information Center's (DDN
       NIC) WHOIS database, or from the "root" account on one of the
       major site machines.  You must include the destination address
       you want on the list, an indication of whether you want to be
       on the mail reflector list or receive weekly digests, the
       electronic mail address and voice telephone number of the site
       contact if it isn't you, and the name, address, and telephone
       number of your organization.  This information should be sent
       The RISKS digest is a component of the ACM Committee on
       Computers and Public Policy, moderated by Peter G. Neumann.  It
       is a discussion forum on risks to the public in computers and
       related systems, and along with discussing computer security
       and privacy issues, has discussed such subjects as the Stark
       incident, the shooting down of the Iranian airliner in the
       Persian Gulf (as it relates to the computerized weapons
       systems), problems in air and railroad traffic control systems,
       software engineering, and so on.  To join the mailing list,
       send a message to RISKS-REQUEST@CSL.SRI.COM.  This list is also
       available in the USENET newsgroup "comp.risks".
       The VIRUS-L list is a forum for the discussion of computer
       virus experiences, protection software, and related topics.
       The list is open to the public, and is implemented as a
       moderated digest.  Most of the information is related to
       personal computers, although some of it may be applicable to
       larger systems.  To subscribe, send the line:
          SUB VIRUS-L your full name
       to the address LISTSERV%LEHIIBM1.BITNET@MITVMA.MIT.EDU.  This
       list is also available via the USENET newsgroup "comp.virus".
       The Computer Underground Digest "is an open forum dedicated to
       sharing information among computerists and to the presentation
       and debate of diverse views."  While not directly a security
       list, it does contain discussions about privacy and other
       security related topics.  The list can be read on USENET as, or to join the mailing list, send mail

Site Security Policy Handbook Working Group [Page 42] RFC 1244 Site Security Handbook July 1991

       to Gordon Myer (
       Submissions may be mailed to:  Networking Mailing Lists
       The TCP-IP mailing list is intended to act as a discussion
       forum for developers and maintainers of implementations of the
       TCP/IP protocol suite.  It also discusses network-related
       security problems when they involve programs providing network
       services, such as "Sendmail".  To join the TCP-IP list, send a
       message to TCP-IP-REQUEST@NISC.SRI.COM.  This list is also
       available in the USENET newsgroup "comp.protocols.tcp-ip".
       SUN-NETS is a discussion list for items pertaining to
       networking on Sun systems.  Much of the discussion is related
       to NFS, NIS (formally Yellow Pages), and name servers.  To
       subscribe, send a message to SUN-NETS-REQUEST@UMIACS.UMD.EDU.
       The USENET groups and also discuss
       security issues. is a moderated group and also
       includes discussions of physical security and locks. is unmoderated.  Response Teams
       Several organizations have formed special groups of people to
       deal with computer security problems.  These teams collect
       information about possible security holes and disseminate it to
       the proper people, track intruders, and assist in recovery from
       security violations.  The teams typically have both electronic
       mail distribution lists as well as a special telephone number
       which can be called for information or to report a problem.
       Many of these teams are members of the CERT System, which is
       coordinated by the National Institute of Standards and
       Technology (NIST), and exists to facilitate the exchange of
       information between the various teams.  DARPA Computer Emergency Response Team
          The Computer Emergency Response Team/Coordination Center
          (CERT/CC) was established in December 1988 by the Defense
          Advanced Research Projects Agency (DARPA) to address
          computer security concerns of research users of the
          Internet.  It is operated by the Software Engineering
          Institute (SEI) at Carnegie-Mellon University (CMU).  The
          CERT can immediately confer with experts to diagnose and
          solve security problems, and also establish and maintain
          communications with the affected computer users and

Site Security Policy Handbook Working Group [Page 43] RFC 1244 Site Security Handbook July 1991

          government authorities as appropriate.
          The CERT/CC serves as a clearing house for the
          identification and repair of security vulnerabilities,
          informal assessments of existing systems, improvement of
          emergency response capability, and both vendor and user
          security awareness.  In addition, the team works with
          vendors of various systems in order to coordinate the fixes
          for security problems.
          The CERT/CC sends out security advisories to the CERT-
          ADVISORY mailing list whenever appropriate.  They also
          operate a 24-hour hotline that can be called to report
          security problems (e.g., someone breaking into your system),
          as well as to obtain current (and accurate) information
          about rumored security problems.
          To join the CERT-ADVISORY mailing list, send a message to
          CERT@CERT.SEI.CMU.EDU and ask to be added to the mailing
          list.  The material sent to this list also appears in the
          USENET newsgroup "".  Past advisories
          are available for anonymous FTP from the host
          CERT.SEI.CMU.EDU.  The 24-hour hotline number is (412) 268-
          The CERT/CC also maintains a CERT-TOOLS list to encourage
          the exchange of information on tools and techniques that
          increase the secure operation of Internet systems.  The
          CERT/CC does not review or endorse the tools described on
          the list.  To subscribe, send a message to CERT-TOOLS-
          REQUEST@CERT.SEI.CMU.EDU and ask to be added to the mailing
          The CERT/CC maintains other generally useful security
          information for anonymous FTP from CERT.SEI.CMU.EDU.  Get
          the README file for a list of what is available.
          For more information, contact:
             Software Engineering Institute
             Carnegie Mellon University
             Pittsburgh, PA  15213-3890
             (412) 268-7090

Site Security Policy Handbook Working Group [Page 44] RFC 1244 Site Security Handbook July 1991  DDN Security Coordination Center
          For DDN users, the Security Coordination Center (SCC) serves
          a function similar to CERT.  The SCC is the DDN's clearing-
          house for host/user security problems and fixes, and works
          with the DDN Network Security Officer.  The SCC also
          distributes the DDN Security Bulletin, which communicates
          information on network and host security exposures, fixes,
          and concerns to security and management personnel at DDN
          facilities.  It is available online, via kermit or anonymous
          FTP, from the host NIC.DDN.MIL, in SCC:DDN-SECURITY-yy-
          nn.TXT (where "yy" is the year and "nn" is the bulletin
          number).  The SCC provides immediate assistance with DDN-
          related host security problems; call (800) 235-3155 (6:00
          a.m. to 5:00 p.m. Pacific Time) or send email to
          SCC@NIC.DDN.MIL.  For 24 hour coverage, call the MILNET
          Trouble Desk (800) 451-7413 or AUTOVON 231-1713.  NIST Computer Security Resource and Response Center
          The National Institute of Standards and Technology (NIST)
          has responsibility within the U.S. Federal Government for
          computer science and technology activities.  NIST has played
          a strong role in organizing the CERT System and is now
          serving as the CERT System Secretariat.  NIST also operates
          a Computer Security Resource and Response Center (CSRC) to
          provide help and information regarding computer security
          events and incidents, as well as to raise awareness about
          computer security vulnerabilities.
          The CSRC team operates a 24-hour hotline, at (301) 975-5200.
          For individuals with access to the Internet, on-line
          publications and computer security information can be
          obtained via anonymous FTP from the host CSRC.NCSL.NIST.GOV
          (  NIST also operates a personal computer
          bulletin board that contains information regarding computer
          viruses as well as other aspects of computer security.  To
          access this board, set your modem to 300/1200/2400 BPS, 1
          stop bit, no parity, and 8-bit characters, and call (301)
          948-5717.  All users are given full access to the board
          immediately upon registering.
          NIST has produced several special publications related to
          computer security and computer viruses in particular; some
          of these publications are downloadable.  For further
          information, contact NIST at the following address:

Site Security Policy Handbook Working Group [Page 45] RFC 1244 Site Security Handbook July 1991

             Computer Security Resource and Response Center
             A-216 Technology
             Gaithersburg, MD 20899
             Telephone: (301) 975-3359
             Electronic Mail:  DOE Computer Incident Advisory Capability (CIAC)
          CIAC is the Department of Energy's (DOE's) Computer Incident
          Advisory Capability.  CIAC is a four-person team of computer
          scientists from Lawrence Livermore National Laboratory
          (LLNL) charged with the primary responsibility of assisting
          DOE sites faced with computer security incidents (e.g.,
          intruder attacks, virus infections, worm attacks, etc.).
          This capability is available to DOE sites on a 24-hour-a-day
          CIAC was formed to provide a centralized response capability
          (including technical assistance), to keep sites informed of
          current events, to deal proactively with computer security
          issues, and to maintain liaisons with other response teams
          and agencies.  CIAC's charter is to assist sites (through
          direct technical assistance, providing information, or
          referring inquiries to other technical experts), serve as a
          clearinghouse for information about threats/known
          incidents/vulnerabilities, develop guidelines for incident
          handling, develop software for responding to
          events/incidents, analyze events and trends, conduct
          training and awareness activities, and alert and advise
          sites about vulnerabilities and potential attacks.
          CIAC's business hours phone number is (415) 422-8193 or FTS
          532-8193.  CIAC's e-mail address is CIAC@TIGER.LLNL.GOV.  NASA Ames Computer Network Security Response Team
          The Computer Network Security Response Team (CNSRT) is NASA
          Ames Research Center's local version of the DARPA CERT.
          Formed in August of 1989, the team has a constituency that
          is primarily Ames users, but it is also involved in
          assisting other NASA Centers and federal agencies.  CNSRT
          maintains liaisons with the DOE's CIAC team and the DARPA
          CERT.  It is also a charter member of the CERT System.  The
          team may be reached by 24 hour pager at (415) 694-0571, or
          by electronic mail to CNSRT@AMES.ARC.NASA.GOV.

Site Security Policy Handbook Working Group [Page 46] RFC 1244 Site Security Handbook July 1991  DDN Management Bulletins
       The DDN Management Bulletin is distributed electronically by
       the DDN NIC under contract to the Defense Communications Agency
       (DCA).  It is a means of communicating official policy,
       procedures, and other information of concern to management
       personnel at DDN facilities.
       The DDN Security Bulletin is distributed electronically by the
       DDN SCC, also under contract to DCA, as a means of
       communicating information on network and host security
       exposures, fixes, and concerns to security and management
       personnel at DDN facilities.
       Anyone may join the mailing lists for these two bulletins by
       sending a message to NIC@NIC.DDN.MIL and asking to be placed on
       the mailing lists.  These messages are also posted to the
       USENET newsgroup "ddn.mgt-bulletin".  For additional
       information, see section 8.7.  System Administration List
       The SYSADM-LIST is a list pertaining exclusively to UNIX system
       administration.  Mail requests to be added to the list to
       SYSADM-LIST-REQUEST@SYSADMIN.COM.  Vendor Specific System Lists
       The SUN-SPOTS and SUN-MANAGERS lists are discussion groups for
       users and administrators of systems supplied by Sun
       Microsystems.  SUN-SPOTS is a fairly general list, discussing
       everything from hardware configurations to simple UNIX
       questions.  To subscribe, send a message to SUN-SPOTS-
       REQUEST@RICE.EDU.  This list is also available in the USENET
       newsgroup "comp.sys.sun".  SUN-MANAGERS is a discussion list
       for Sun system administrators and covers all aspects of Sun
       system administration.  To subscribe, send a message to SUN-
       The APOLLO list discusses the HP/Apollo system and its
       software.  To subscribe, send a message to APOLLO-
       REQUEST@UMIX.CC.UMICH.EDU.  APOLLO-L is a similar list which
       can be subscribed to by sending
          SUB APOLLO-L your full name

Site Security Policy Handbook Working Group [Page 47] RFC 1244 Site Security Handbook July 1991

       HPMINI-L pertains to the Hewlett-Packard 9000 series and HP/UX
       operating system.  To subscribe, send
          SUB HPMINI-L your full name
       INFO-IBMPC discusses IBM PCs and compatibles, as well as MS-
       DOS.  To subscribe, send a note to INFO-IBMPC-REQUEST@WSMR-
       There are numerous other mailing lists for nearly every popular
       computer or workstation in use today.  For a complete list,
       obtain the file "netinfo/interest-groups" via anonymous FTP
       from the host FTP.NISC.SRI.COM.  Professional Societies and Journals
       The IEEE Technical Committee on Security & Privacy publishes a
       quarterly magazine, "CIPHER".
          IEEE Computer Society,
          1730 Massachusetts Ave. N.W.
          Washington, DC  2036-1903
       The ACM SigSAC (Special Interest Group on Security, Audit, and
       Controls) publishes a quarterly magazine, "SIGSAC Review".
          Association for Computing Machinery
          11 West 42nd St.
          New York, N.Y.  10036
       The Information Systems Security Association publishes a
       quarterly magazine called "ISSA Access".
          Information Systems Security Association
          P.O. Box 9457
          Newport Beach, CA  92658
       "Computers and Security" is an "international journal for the
       professional involved with computer security, audit and
       control, and data integrity."

Site Security Policy Handbook Working Group [Page 48] RFC 1244 Site Security Handbook July 1991

          $266/year, 8 issues (1990)
          Elsevier Advanced Technology
          Journal Information Center
          655 Avenue of the Americas
          New York, NY 10010
       The "Data Security Letter" is published "to help data security
       professionals by providing inside information and knowledgable
       analysis of developments in computer and communications
          $690/year, 9 issues (1990)
          Data Security Letter
          P.O. Box 1593
          Palo Alto, CA 94302
 3.9.8  Problem Reporting Tools  Auditing
       Auditing is an important tool that can be used to enhance the
       security of your installation.  Not only does it give you a
       means of identifying who has accessed your system (and may have
       done something to it) but it also gives you an indication of
       how your system is being used (or abused) by authorized users
       and attackers alike.  In addition, the audit trail
       traditionally kept by computer systems can become an invaluable
       piece of evidence should your system be penetrated.  Verify Security
          An audit trail shows how the system is being used from day
          to day.  Depending upon how your site audit log is
          configured, your log files should show a range of access
          attempts that can show what normal system usage should look
          like.  Deviation from that normal usage could be the result
          of penetration from an outside source using an old or stale
          user account.  Observing a deviation in logins, for example,
          could be your first indication that something unusual is
          happening.  Verify Software Configurations
          One of the ruses used by attackers to gain access to a
          system is by the insertion of a so-called Trojan Horse
          program.  A Trojan Horse program can be a program that does

Site Security Policy Handbook Working Group [Page 49] RFC 1244 Site Security Handbook July 1991

          something useful, or merely something interesting.  It
          always does something unexpected, like steal passwords or
          copy files without your knowledge [25].  Imagine a Trojan
          login program that prompts for username and password in the
          usual way, but also writes that information to a special
          file that the attacker can come back and read at will.
          Imagine a Trojan Editor program that, despite the file
          permissions you have given your files, makes copies of
          everything in your directory space without you knowing about
          This points out the need for configuration management of the
          software that runs on a system, not as it is being
          developed, but as it is in actual operation.  Techniques for
          doing this range from checking each command every time it is
          executed against some criterion (such as a cryptoseal,
          described above) or merely checking the date and time stamp
          of the executable.  Another technique might be to check each
          command in batch mode at midnight.  Tools
       COPS is a security tool for system administrators that checks
       for numerous common security problems on UNIX systems [27].
       COPS is a collection of shell scripts and C programs that can
       easily be run on almost any UNIX variant.  Among other things,
       it checks the following items and sends the results to the
       system administrator:
  1. Checks "/dev/kmem" and other devices for world


  1. Checks special or important files and directories for

"bad" modes (world writable, etc.).

  1. Checks for easily-guessed passwords.
  1. Checks for duplicate user ids, invalid fields in the

password file, etc..

  1. Checks for duplicate group ids, invalid fields in the

group file, etc..

  1. Checks all users' home directories and their ".cshrc",

".login", ".profile", and ".rhosts" files for security

  1. Checks all commands in the "/etc/rc" files and "cron"

Site Security Policy Handbook Working Group [Page 50] RFC 1244 Site Security Handbook July 1991

            files for world writability.
  1. Checks for bad "root" paths, NFS file systems exported

to the world, etc..

  1. Includes an expert system that checks to see if a given

user (usually "root") can be compromised, given that

            certain rules are true.
  1. Checks for changes in the setuid status of programs on the


       The COPS package is available from the "comp.sources.unix"
       archive on "", and also from the UNIX-SW repository
       on the MILNET host "".
 3.9.9  Communication Among Administrators  Secure Operating Systems
       The following list of products and vendors is adapted from the
       National Computer Security Center's (NCSC) Evaluated Products
       List.  They represent those companies who have either received
       an evaluation from the NCSC or are in the process of a product
       evaluation.  This list is not complete, but it is
       representative of those operating systems and add on components
       available in the commercial marketplace.
       For a more detailed listing of the current products appearing
       in the NCSC EPL, contact the NCSC at:
          National Computer Security Center
          9800 Savage Road
          Fort George G. Meade, MD  20755-6000
          (301) 859-4458

Site Security Policy Handbook Working Group [Page 51] RFC 1244 Site Security Handbook July 1991

                                                Version    Evaluation

Evaluated Product Vendor Evaluated Class

Secure Communications Honeywell Information 2.1 A1 Processor (SCOMP) Systems, Inc.

Multics Honeywell Information MR11.0 B2

                              Systems, Inc.

System V/MLS 1.1.2 on UNIX AT&T 1.1.2 B1 System V 3.1.1 on AT&T 3B2/500and 3B2/600

OS 1100 Unisys Corp. Security B1

                                                       Release 1

MPE V/E Hewlett-Packard Computer G.03.04 C2

                              Systems Division

AOS/VS on MV/ECLIPSE series Data General Corp. 7.60 C2


MVS/XA with RACF IBM Corp. 2.2,2.3 C2

AX/VMS Digital Equipment Corp. 4.3 C2

NOS Control Data Corp. NOS

                                                         Security  C2
                                                     Eval Product

TOP SECRET CGA Software Products 3.0/163 C2

                              Group, Inc.

Access Control Facility 2 SKK, Inc. 3.1.3 C2

UTX/32S Gould, Inc. Computer 1.0 C2

                              Systems Division

A Series MCP/AS with Unisys Corp. 3.7 C2 InfoGuard Security Enhancements

Primos Prime Computer, Inc. 21.0.1DODC2A C2 Resource Access Control IBM Corp. 1.5 C1 Facility (RACF)

Site Security Policy Handbook Working Group [Page 52] RFC 1244 Site Security Handbook July 1991

                                                Version      Candidate

Candidate Product Vendor Evaluated Class

Boeing MLS LAN Boeing Aerospace A1 M1

Trusted XENIX Trusted Information

                              Systems, Inc.                     B2


System V/MLS AT&T B1

VM/SP with RACF IBM Corp. 5/1.8.2 C2 Wang SVS/OS with CAP Wang Laboratories, Inc. 1.0 C2  Obtaining Fixes for Known Problems
       It goes without saying that computer systems have bugs.  Even
       operating systems, upon which we depend for protection of our
       data, have bugs.  And since there are bugs, things can be
       broken, both maliciously and accidentally.  It is important
       that whenever bugs are discovered, a should fix be identified
       and implemented as soon as possible.  This should minimize any
       exposure caused by the bug in the first place.
       A corollary to the bug problem is: from whom do I obtain the
       fixes?  Most systems have some support from the manufacturer or
       supplier.  Fixes coming from that source tend to be implemented
       quickly after receipt.  Fixes for some problems are often
       posted on the network and are left to the system administrators
       to incorporate as they can.  The problem is that one wants to
       have faith that the fix will close the hole and not introduce
       any others.  We will tend to trust that the manufacturer's
       fixes are better than those that are posted on the net.  Sun Customer Warning System
       Sun Microsystems has established a Customer Warning System
       (CWS) for handling security incidents.  This is a formal
       process which includes:
  1. Having a well advertised point of contact in Sun

for reporting security problems.

  1. Pro-actively alerting customers of worms, viruses,

or other security holes that could affect their systems.

  1. Distributing the patch (or work-around) as quickly

as possible.

Site Security Policy Handbook Working Group [Page 53] RFC 1244 Site Security Handbook July 1991

       They have created an electronic mail address, SECURITY-
       ALERT@SUN.COM, which will enable customers to report security
       problems.  A voice-mail backup is available at (415) 688-9081.
       A "Security Contact" can be designated by each customer site;
       this person will be contacted by Sun in case of any new
       security problems.  For more information, contact your Sun
       representative.  Trusted Archive Servers
       Several sites on the Internet maintain large repositories of
       public-domain and freely distributable software, and make this
       material available for anonymous FTP.  This section describes
       some of the larger repositories.  Note that none of these
       servers implements secure checksums or anything else
       guaranteeing the integrity of their data.  Thus, the notion of
       "trust" should be taken as a somewhat limited definition.  Sun Fixes on UUNET
          Sun Microsystems has contracted with UUNET Communications
          Services, Inc., to make fixes for bugs in Sun software
          available via anonymous FTP.  You can access these fixes by
          using the "ftp" command to connect to the host FTP.UU.NET.
          Then change into the directory "sun-dist/security", and
          obtain a directory listing.  The file "README" contains a
          brief description of what each file in this directory
          contains, and what is required to install the fix.  Berkeley Fixes
          The University of California at Berkeley also makes fixes
          available via anonymous FTP; these fixes pertain primarily
          to the current release of BSD UNIX (currently, release 4.3).
          However, even if you are not running their software, these
          fixes are still important, since many vendors (Sun, DEC,
          Sequent, etc.) base their software on the Berkeley releases.
          The Berkeley fixes are available for anonymous FTP from the
          host UCBARPA.BERKELEY.EDU in the directory "4.3/ucb-fixes".
          The file "INDEX" in this directory describes what each file
          contains.  They are also available from UUNET (see section

          Berkeley also distributes new versions of "sendmail" and
          "named" from this machine.  New versions of these commands
          are stored in the "4.3" directory, usually in the files
          "sendmail.tar.Z" and "bind.tar.Z", respectively.

Site Security Policy Handbook Working Group [Page 54] RFC 1244 Site Security Handbook July 1991  Simtel-20 and UUNET
          The two largest general-purpose software repositories on the
          Internet are the hosts WSMR-SIMTEL20.ARMY.MIL and
          WSMR-SIMTEL20.ARMY.MIL is a TOPS-20 machine operated by the
          U.S. Army at White Sands Missile Range (WSMR), New Mexico.
          The directory "pd2:<unix-c>" contains a large amount of UNIX
          software, primarily taken from the "comp.sources"
          newsgroups.  The directories "pd1:<msdos>" and
          "pd2:<msdos2>" contains software for IBM PC systems, and
          "pd3:<macintosh>" contains software for the Apple Macintosh.
          FTP.UU.NET is operated by UUNET Communications Services,
          Inc. in Falls Church, Virginia.  This company sells Internet
          and USENET access to sites all over the country (and
          internationally).  The software posted to the following
          USENET source newsgroups is stored here, in directories of
          the same name:
          Numerous other distributions, such as all the freely
          distributable Berkeley UNIX source code, Internet Request
          for Comments (RFCs), and so on are also stored on this
          system.  Vendors
          Many vendors make fixes for bugs in their software available
          electronically, either via mailing lists or via anonymous
          FTP.  You should contact your vendor to find out if they
          offer this service, and if so, how to access it.  Some
          vendors that offer these services include Sun Microsystems
          (see above), Digital Equipment Corporation (DEC), the
          University of California at Berkeley (see above), and Apple
          Computer [5, CURRY].

Site Security Policy Handbook Working Group [Page 55] RFC 1244 Site Security Handbook July 1991

4. Types of Security Procedures

4.1 System Security Audits

 Most businesses undergo some sort of annual financial auditing as a
 regular part of their business life.  Security audits are an
 important part of running any computing environment.  Part of the
 security audit should be a review of any policies that concern system
 security, as well as the mechanisms that are put in place to enforce
 4.1.1   Organize Scheduled Drills
    Although not something that would be done each day or week,
    scheduled drills may be conducted to determine if the procedures
    defined are adequate for the threat to be countered.  If your
    major threat is one of natural disaster, then a drill would be
    conducted to verify your backup and recovery mechanisms.  On the
    other hand, if your greatest threat is from external intruders
    attempting to penetrate your system, a drill might be conducted to
    actually try a penetration to observe the effect of the policies.
    Drills are a valuable way to test that your policies and
    procedures are effective.  On the other hand, drills can be time-
    consuming and disruptive to normal operations.  It is important to
    weigh the benefits of the drills against the possible time loss
    which may be associated with them.
 4.1.2  Test Procedures
    If the choice is made to not to use scheduled drills to examine
    your entire security procedure at one time, it is important to
    test individual procedures frequently.  Examine your backup
    procedure to make sure you can recover data from the tapes.  Check
    log files to be sure that information which is supposed to be
    logged to them is being logged to them, etc..
    When a security audit is mandated, great care should be used in
    devising tests of the security policy.  It is important to clearly
    identify what is being tested, how the test will be conducted, and
    results expected from the test.  This should all be documented and
    included in or as an adjunct to the security policy document
    It is important to test all aspects of the security policy, both
    procedural and automated, with a particular emphasis on the
    automated mechanisms used to enforce the policy.  Tests should be
    defined to ensure a comprehensive examination of policy features,

Site Security Policy Handbook Working Group [Page 56] RFC 1244 Site Security Handbook July 1991

    that is, if a test is defined to examine the user logon process,
    it should be explicitly stated that both valid and invalid user
    names and passwords will be used to demonstrate proper operation
    of the logon program.
    Keep in mind that there is a limit to the reasonableness of tests.
    The purpose of testing is to ensure confidence that the security
    policy is being correctly enforced, and not to "prove" the
    absoluteness of the system or policy.  The goal should be to
    obtain some assurance that the reasonable and credible controls
    imposed by your security policy are adequate.

4.2 Account Management Procedures

 Procedures to manage accounts are important in preventing
 unauthorized access to your system.  It is necessary to decide
 several things: Who may have an account on the system?  How long may
 someone have an account without renewing his or her request?  How do
 old accounts get removed from the system?  The answers to all these
 questions should be explicitly set out in the policy.
 In addition to deciding who may use a system, it may be important to
 determine what each user may use the system for (is personal use
 allowed, for example).  If you are connected to an outside network,
 your site or the network management may have rules about what the
 network may be used for.  Therefore, it is important for any security
 policy to define an adequate account management procedure for both
 administrators and users.  Typically, the system administrator would
 be responsible for creating and deleting user accounts and generally
 maintaining overall control of system use.  To some degree, account
 management is also the responsibility of each system user in the
 sense that the user should observe any system messages and events
 that may be indicative of a policy violation.  For example, a message
 at logon that indicates the date and time of the last logon should be
 reported by the user if it indicates an unreasonable time of last

4.3 Password Management Procedures

 A policy on password management may be important if your site wishes
 to enforce secure passwords.  These procedures may range from asking
 or forcing users to change their passwords occasionally to actively
 attempting to break users' passwords and then informing the user of
 how easy it was to do.  Another part of password management policy
 covers who may distribute passwords - can users give their passwords
 to other users?
 Section 2.3 discusses some of the policy issues that need to be

Site Security Policy Handbook Working Group [Page 57] RFC 1244 Site Security Handbook July 1991

 decided for proper password management.  Regardless of the policies,
 password management procedures need to be carefully setup to avoid
 disclosing passwords.  The choice of initial passwords for accounts
 is critical.  In some cases, users may never login to activate an
 account; thus, the choice of the initial password should not be
 easily guessed.  Default passwords should never be assigned to
 accounts: always create new passwords for each user.  If there are
 any printed lists of passwords, these should be kept off-line in
 secure locations; better yet, don't list passwords.
 4.3.1  Password Selection
    Perhaps the most vulnerable part of any computer system is the
    account password.  Any computer system, no matter how secure it is
    from network or dial-up attack, Trojan horse programs, and so on,
    can be fully exploited by an intruder if he or she can gain access
    via a poorly chosen password.  It is important to define a good
    set of rules for password selection, and distribute these rules to
    all users.  If possible, the software which sets user passwords
    should be modified to enforce as many of the rules as possible.
    A sample set of guidelines for password selection is shown below:
  1. DON'T use your login name in any form (as-is,

reversed, capitalized, doubled, etc.).

  1. DON'T use your first, middle, or last name in any form.
  1. DON'T use your spouse's or child's name.
  1. DON'T use other information easily obtained about you.

This includes license plate numbers, telephone numbers,

         social security numbers, the make of your automobile,
         the name of the street you live on, etc..
  1. DON'T use a password of all digits, or all the same


  1. DON'T use a word contained in English or foreign

language dictionaries, spelling lists, or other

         lists of words.
  1. DON'T use a password shorter than six characters.
  1. DO use a password with mixed-case alphabetics.
  1. DO use a password with non-alphabetic characters (digits

or punctuation).

Site Security Policy Handbook Working Group [Page 58] RFC 1244 Site Security Handbook July 1991

  1. DO use a password that is easy to remember, so you don't

have to write it down.

  1. DO use a password that you can type quickly, without

having to look at the keyboard.

    Methods of selecting a password which adheres to these guidelines
  1. Choose a line or two from a song or poem, and use the

first letter of each word.

  1. Alternate between one consonant and one or two vowels, up

to seven or eight characters. This provides nonsense

         words which are usually pronounceable, and thus easily
  1. Choose two short words and concatenate them together with

a punctuation character between them.

    Users should also be told to change their password periodically,
    usually every three to six months.  This makes sure that an
    intruder who has guessed a password will eventually lose access,
    as well as invalidating any list of passwords he/she may have
    obtained.  Many systems enable the system administrator to force
    users to change their passwords after an expiration period; this
    software should be enabled if your system supports it [5, CURRY].
    Some systems provide software which forces users to change their
    passwords on a regular basis.  Many of these systems also include
    password generators which provide the user with a set of passwords
    to choose from.  The user is not permitted to make up his or her
    own password.  There are arguments both for and against systems
    such as these.  On the one hand, by using generated passwords,
    users are prevented from selecting insecure passwords.  On the
    other hand, unless the generator is good at making up easy to
    remember passwords, users will begin writing them down in order to
    remember them.
 4.3.2  Procedures for Changing Passwords
    How password changes are handled is important to keeping passwords
    secure.  Ideally, users should be able to change their own
    passwords on-line.  (Note that password changing programs are a
    favorite target of intruders.  See section 4.4 on configuration
    management for further information.)
    However, there are exception cases which must be handled

Site Security Policy Handbook Working Group [Page 59] RFC 1244 Site Security Handbook July 1991

    carefully.  Users may forget passwords and not be able to get onto
    the system.  The standard procedure is to assign the user a new
    password.  Care should be taken to make sure that the real person
    is requesting the change and gets the new password.  One common
    trick used by intruders is to call or message to a system
    administrator and request a new password. Some external form of
    verification should be used before the password is assigned.  At
    some sites, users are required to show up in person with ID.
    There may also be times when many passwords need to be changed.
    If a system is compromised by an intruder, the intruder may be
    able to steal a password file and take it off the system.  Under
    these circumstances, one course of action is to change all
    passwords on the system.  Your site should have procedures for how
    this can be done quickly and efficiently.  What course you choose
    may depend on the urgency of the problem.  In the case of a known
    attack with damage, you may choose to forcibly disable all
    accounts and assign users new passwords before they come back onto
    the system.  In some places, users are sent a message telling them
    that they should change their passwords, perhaps within a certain
    time period.  If the password isn't changed before the time period
    expires, the account is locked.
    Users should be aware of what the standard procedure is for
    passwords when a security event has occurred.  One well-known
    spoof reported by the Computer Emergency Response Team (CERT)
    involved messages sent to users, supposedly from local system
    administrators, requesting them to immediately change their
    password to a new value provided in the message [24].  These
    messages were not from the administrators, but from intruders
    trying to steal accounts.  Users should be warned to immediately
    report any suspicious requests such as this to site

4.4 Configuration Management Procedures

 Configuration management is generally applied to the software
 development process.  However, it is certainly applicable in a
 operational sense as well.  Consider that the since many of the
 system level programs are intended to enforce the security policy, it
 is important that these be "known" as correct.  That is, one should
 not allow system level programs (such as the operating system, etc.)
 to be changed arbitrarily.  At very least, the procedures should
 state who is authorized to make changes to systems, under what
 circumstances, and how the changes should be documented.
 In some environments, configuration management is also desirable as
 applied to physical configuration of equipment.  Maintaining valid

Site Security Policy Handbook Working Group [Page 60] RFC 1244 Site Security Handbook July 1991

 and authorized hardware configuration should be given due
 consideration in your security policy.
 4.4.1  Non-Standard Configurations
    Occasionally, it may be beneficial to have a slightly non-standard
    configuration in order to thwart the "standard" attacks used by
    some intruders.  The non-standard parts of the configuration might
    include different password encryption algorithms, different
    configuration file locations, and rewritten or functionally
    limited system commands.
    Non-standard configurations, however, also have their drawbacks.
    By changing the "standard" system, these modifications make
    software maintenance more difficult by requiring extra
    documentation to be written, software modification after operating
    system upgrades, and, usually, someone with special knowledge of
    the changes.
    Because of the drawbacks of non-standard configurations, they are
    often only used in environments with a "firewall" machine (see
    section 3.9.1).  The firewall machine is modified in non-standard
    ways since it is susceptible to attack, while internal systems
    behind the firewall are left in their standard configurations.

5. Incident Handling

5.1 Overview

 This section of the document will supply some guidance to be applied
 when a computer security event is in progress on a machine, network,
 site, or multi-site environment.  The operative philosophy in the
 event of a breach of computer security, whether it be an external
 intruder attack or a disgruntled employee, is to plan for adverse
 events in advance.  There is no substitute for creating contingency
 plans for the types of events described above.
 Traditional computer security, while quite important in the overall
 site security plan, usually falls heavily on protecting systems from
 attack, and perhaps monitoring systems to detect attacks.  Little
 attention is usually paid for how to actually handle the attack when
 it occurs.  The result is that when an attack is in progress, many
 decisions are made in haste and can be damaging to tracking down the
 source of the incident, collecting evidence to be used in prosecution
 efforts, preparing for the recovery of the system, and protecting the
 valuable data contained on the system.

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 5.1.1  Have a Plan to Follow in Case of an Incident
    Part of handling an incident is being prepared to respond before
    the incident occurs.  This includes establishing a suitable level
    of protections, so that if the incident becomes severe, the damage
    which can occur is limited.  Protection includes preparing
    incident handling guidelines or a contingency response plan for
    your organization or site.  Having written plans eliminates much
    of the ambiguity which occurs during an incident, and will lead to
    a more appropriate and thorough set of responses.  Second, part of
    protection is preparing a method of notification, so you will know
    who to call and the relevant phone numbers.  It is important, for
    example, to conduct "dry runs," in which your computer security
    personnel, system administrators, and managers simulate handling
    an incident.
    Learning to respond efficiently to an incident is important for
    numerous reasons.  The most important benefit is directly to human
    beings--preventing loss of human life.  Some computing systems are
    life critical systems, systems on which human life depends (e.g.,
    by controlling some aspect of life-support in a hospital or
    assisting air traffic controllers).
    An important but often overlooked benefit is an economic one.
    Having both technical and managerial personnel respond to an
    incident requires considerable resources, resources which could be
    utilized more profitably if an incident did not require their
    services.  If these personnel are trained to handle an incident
    efficiently, less of their time is required to deal with that
    A third benefit is protecting classified, sensitive, or
    proprietary information.  One of the major dangers of a computer
    security incident is that information may be irrecoverable.
    Efficient incident handling minimizes this danger.  When
    classified information is involved, other government regulations
    may apply and must be integrated into any plan for incident
    A fourth benefit is related to public relations.  News about
    computer security incidents tends to be damaging to an
    organization's stature among current or potential clients.
    Efficient incident handling minimizes the potential for negative
    A final benefit of efficient incident handling is related to legal
    issues.  It is possible that in the near future organizations may
    be sued because one of their nodes was used to launch a network

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    attack.  In a similar vein, people who develop patches or
    workarounds may be sued if the patches or workarounds are
    ineffective, resulting in damage to systems, or if the patches or
    workarounds themselves damage systems.  Knowing about operating
    system vulnerabilities and patterns of attacks and then taking
    appropriate measures is critical to circumventing possible legal
 5.1.2  Order of Discussion in this Session Suggests an Order for
        a Plan
    This chapter is arranged such that a list may be generated from
    the Table of Contents to provide a starting point for creating a
    policy for handling ongoing incidents.  The main points to be
    included in a policy for handling incidents are:
       o Overview (what are the goals and objectives in handling the
       o Evaluation (how serious is the incident).
       o Notification (who should be notified about the incident).
       o Response (what should the response to the incident be).
       o Legal/Investigative (what are the legal and prosecutorial
         implications of the incident).
       o Documentation Logs (what records should be kept from before,
         during, and after the incident).
    Each of these points is important in an overall plan for handling
    incidents.  The remainder of this chapter will detail the issues
    involved in each of these topics, and provide some guidance as to
    what should be included in a site policy for handling incidents.
    5.1.3  Possible Goals and Incentives for Efficient Incident
    As in any set of pre-planned procedures, attention must be placed
    on a set of goals to be obtained in handling an incident.  These
    goals will be placed in order of importance depending on the site,
    but one such set of goals might be:
       Assure integrity of (life) critical systems.
       Maintain and restore data.
       Maintain and restore service.
       Figure out how it happened.
       Avoid escalation and further incidents.
       Avoid negative publicity.
       Find out who did it.
       Punish the attackers.

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    It is important to prioritize actions to be taken during an
    incident well in advance of the time an incident occurs.
    Sometimes an incident may be so complex that it is impossible to
    do everything at once to respond to it; priorities are essential.
    Although priorities will vary from institution-to-institution, the
    following suggested priorities serve as a starting point for
    defining an organization's response:
       o Priority one -- protect human life and people's
         safety; human life always has precedence over all
         other considerations.
       o Priority two -- protect classified and/or sensitive
         data (as regulated by your site or by government
       o Priority three -- protect other data, including
         proprietary, scientific, managerial and other data,
         because loss of data is costly in terms of resources.
       o Priority four -- prevent damage to systems (e.g., loss
         or alteration of system files, damage to disk drives,
         etc.); damage to systems can result in costly down
         time and recovery.
       o Priority five -- minimize disruption of computing
         resources; it is better in many cases to shut a system
         down or disconnect from a network than to risk damage
         to data or systems.
    An important implication for defining priorities is that once
    human life and national security considerations have been
    addressed, it is generally more important to save data than system
    software and hardware.  Although it is undesirable to have any
    damage or loss during an incident, systems can be replaced; the
    loss or compromise of data (especially classified data), however,
    is usually not an acceptable outcome under any circumstances.
    Part of handling an incident is being prepared to respond before
    the incident occurs.  This includes establishing a suitable level
    of protections so that if the incident becomes severe, the damage
    which can occur is limited.  Protection includes preparing
    incident handling guidelines or a contingency response plan for
    your organization or site.  Written plans eliminate much of the
    ambiguity which occurs during an incident, and will lead to a more
    appropriate and thorough set of responses.  Second, part of
    protection is preparing a method of notification so you will know
    who to call and how to contact them.  For example, every member of

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    the Department of Energy's CIAC Team carries a card with every
    other team member's work and home phone numbers, as well as pager
    numbers.  Third, your organization or site should establish backup
    procedures for every machine and system.  Having backups
    eliminates much of the threat of even a severe incident, since
    backups preclude serious data loss.  Fourth, you should set up
    secure systems.  This involves eliminating vulnerabilities,
    establishing an effective password policy, and other procedures,
    all of which will be explained later in this document.  Finally,
    conducting training activities is part of protection.  It is
    important, for example, to conduct "dry runs," in which your
    computer security personnel, system administrators, and managers
    simulate handling an incident.
 5.1.4  Local Policies and Regulations Providing Guidance
    Any plan for responding to security incidents should be guided by
    local policies and regulations.  Government and private sites that
    deal with classified material have specific rules that they must
    The policies your site makes about how it responds to incidents
    (as discussed in sections 2.4 and 2.5) will shape your response.
    For example, it may make little sense to create mechanisms to
    monitor and trace intruders if your site does not plan to take
    action against the intruders if they are caught.  Other
    organizations may have policies that affect your plans.  Telephone
    companies often release information about telephone traces only to
    law enforcement agencies.
    Section 5.5 also notes that if any legal action is planned, there
    are specific guidelines that must be followed to make sure that
    any information collected can be used as evidence.

5.2 Evaluation

 5.2.1  Is It Real?
    This stage involves determining the exact problem.  Of course
    many, if not most, signs often associated with virus infections,
    system intrusions, etc., are simply anomalies such as hardware
    failures.  To assist in identifying whether there really is an
    incident, it is usually helpful to obtain and use any detection
    software which may be available.  For example, widely available
    software packages can greatly assist someone who thinks there may
    be a virus in a Macintosh computer.  Audit information is also
    extremely useful, especially in determining whether there is a
    network attack.  It is extremely important to obtain a system

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    snapshot as soon as one suspects that something is wrong.  Many
    incidents cause a dynamic chain of events to occur, and an initial
    system snapshot may do more good in identifying the problem and
    any source of attack than most other actions which can be taken at
    this stage.  Finally, it is important to start a log book.
    Recording system events, telephone conversations, time stamps,
    etc., can lead to a more rapid and systematic identification of
    the problem, and is the basis for subsequent stages of incident
    There are certain indications or "symptoms" of an incident which
    deserve special attention:
       o System crashes.
       o New user accounts (e.g., the account RUMPLESTILTSKIN
         has unexplainedly been created), or high activity on
         an account that has had virtually no activity for
       o New files (usually with novel or strange file names,
         such as data.xx or k).
       o Accounting discrepancies (e.g., in a UNIX system you
         might notice that the accounting file called
         /usr/admin/lastlog has shrunk, something that should
         make you very suspicious that there may be an
       o Changes in file lengths or dates (e.g., a user should
         be suspicious if he/she observes that the .EXE files in
         an MS DOS computer have unexplainedly grown
         by over 1800 bytes).
       o Attempts to write to system (e.g., a system manager
         notices that a privileged user in a VMS system is
         attempting to alter RIGHTSLIST.DAT).
       o Data modification or deletion (e.g., files start to
       o Denial of service (e.g., a system manager and all
         other users become locked out of a UNIX system, which
         has been changed to single user mode).
       o Unexplained, poor system performance (e.g., system
         response time becomes unusually slow).
       o Anomalies (e.g., "GOTCHA" is displayed on a display
         terminal or there are frequent unexplained "beeps").
       o Suspicious probes (e.g., there are numerous
         unsuccessful login attempts from another node).
       o Suspicious browsing (e.g., someone becomes a root user
         on a UNIX system and accesses file after file in one
         user's account, then another's).
    None of these indications is absolute "proof" that an incident is

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    occurring, nor are all of these indications normally observed when
    an incident occurs.  If you observe any of these indications,
    however, it is important to suspect that an incident might be
    occurring, and act accordingly.  There is no formula for
    determining with 100 percent accuracy that an incident is
    occurring (possible exception: when a virus detection package
    indicates that your machine has the nVIR virus and you confirm
    this by examining contents of the nVIR resource in your Macintosh
    computer, you can be very certain that your machine is infected).
    It is best at this point to collaborate with other technical and
    computer security personnel to make a decision as a group about
    whether an incident is occurring.
 5.2.2  Scope
    Along with the identification of the incident is the evaluation of
    the scope and impact of the problem.  It is important to correctly
    identify the boundaries of the incident in order to effectively
    deal with it.  In addition, the impact of an incident will
    determine its priority in allocating resources to deal with the
    event.  Without an indication of the scope and impact of the
    event, it is difficult to determine a correct response.
    In order to identify the scope and impact, a set of criteria
    should be defined which is appropriate to the site and to the type
    of connections available.  Some of the issues are:
       o Is this a multi-site incident?
       o Are many computers at your site effected by this
       o Is sensitive information involved?
       o What is the entry point of the incident (network,
         phone line, local terminal, etc.)?
       o Is the press involved?
       o What is the potential damage of the incident?
       o What is the estimated time to close out the incident?
       o What resources could be required
         to handle the incident?

5.3 Possible Types of Notification

 When you have confirmed that an incident is occurring, the
 appropriate personnel must be notified.  Who and how this
 notification is achieved is very important in keeping the event under
 control both from a technical and emotional standpoint.

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 5.3.1  Explicit
    First of all, any notification to either local or off-site
    personnel must be explicit.  This requires that any statement (be
    it an electronic mail message, phone call, or fax) provides
    information about the incident that is clear, concise, and fully
    qualified.  When you are notifying others that will help you to
    handle an event, a "smoke screen" will only divide the effort and
    create confusion.  If a division of labor is suggested, it is
    helpful to provide information to each section about what is being
    accomplished in other efforts.  This will not only reduce
    duplication of effort, but allow people working on parts of the
    problem to know where to obtain other information that would help
    them resolve a part of the incident.
 5.3.2  Factual
    Another important consideration when communicating about the
    incident is to be factual.  Attempting to hide aspects of the
    incident by providing false or incomplete information may not only
    prevent a successful resolution to the incident, but may even
    worsen the situation.  This is especially true when the press is
    involved.  When an incident severe enough to gain press attention
    is ongoing, it is likely that any false information you provide
    will not be substantiated by other sources.  This will reflect
    badly on the site and may create enough ill-will between the site
    and the press to damage the site's public relations.
 5.3.3  Choice of Language
    The choice of language used when notifying people about the
    incident can have a profound effect on the way that information is
    received.  When you use emotional or inflammatory terms, you raise
    the expectations of damage and negative outcomes of the incident.
    It is important to remain calm both in written and spoken
    Another issue associated with the choice of language is the
    notification to non-technical or off-site personnel.  It is
    important to accurately describe the incident without undue alarm
    or confusing messages.  While it is more difficult to describe the
    incident to a non-technical audience, it is often more important.
    A non-technical description may be required for upper-level
    management, the press, or law enforcement liaisons.  The
    importance of these notifications cannot be underestimated and may
    make the difference between handling the incident properly and
    escalating to some higher level of damage.

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 5.3.4  Notification of Individuals
       o Point of Contact (POC) people (Technical, Administrative,
         Response Teams, Investigative, Legal, Vendors, Service
         providers), and which POCs are visible to whom.
       o Wider community (users).
       o Other sites that might be affected.
    Finally, there is the question of who should be notified during
    and after the incident.  There are several classes of individuals
    that need to be considered for notification.  These are the
    technical personnel, administration, appropriate response teams
    (such as CERT or CIAC), law enforcement, vendors, and other
    service providers.  These issues are important for the central
    point of contact, since that is the person responsible for the
    actual notification of others (see section 5.3.6 for further
    information).  A list of people in each of these categories is an
    important time saver for the POC during an incident.  It is much
    more difficult to find an appropriate person during an incident
    when many urgent events are ongoing.
    In addition to the people responsible for handling part of the
    incident, there may be other sites affected by the incident (or
    perhaps simply at risk from the incident).  A wider community of
    users may also benefit from knowledge of the incident.  Often, a
    report of the incident once it is closed out is appropriate for
    publication to the wider user community.
 5.3.5  Public Relations - Press Releases
    One of the most important issues to consider is when, who, and how
    much to release to the general public through the press.  There
    are many issues to consider when deciding this particular issue.
    First and foremost, if a public relations office exists for the
    site, it is important to use this office as liaison to the press.
    The public relations office is trained in the type and wording of
    information released, and will help to assure that the image of
    the site is protected during and after the incident (if possible).
    A public relations office has the advantage that you can
    communicate candidly with them, and provide a buffer between the
    constant press attention and the need of the POC to maintain
    control over the incident.
    If a public relations office is not available, the information
    released to the press must be carefully considered.  If the
    information is sensitive, it may be advantageous to provide only
    minimal or overview information to the press.  It is quite
    possible that any information provided to the press will be

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    quickly reviewed by the perpetrator of the incident.  As a
    contrast to this consideration, it was discussed above that
    misleading the press can often backfire and cause more damage than
    releasing sensitive information.
    While it is difficult to determine in advance what level of detail
    to provide to the press, some guidelines to keep in mind are:
       o Keep the technical level of detail low.  Detailed
         information about the incident may provide enough
         information for copy-cat events or even damage the
         site's ability to prosecute once the event is over.
       o Keep the speculation out of press statements.
         Speculation of who is causing the incident or the
         motives are very likely to be in error and may cause
         an inflamed view of the incident.
       o Work with law enforcement professionals to assure that
         evidence is protected.  If prosecution is involved,
         assure that the evidence collected is not divulged to
         the press.
       o Try not to be forced into a press interview before you are
         prepared.  The popular press is famous for the "2am"
         interview, where the hope is to catch the interviewee off
         guard and obtain information otherwise not available.
       o Do not allow the press attention to detract from the
         handling of the event.  Always remember that the successful
         closure of an incident is of primary importance.
 5.3.6  Who Needs to Get Involved?
    There now exists a number of incident response teams (IRTs) such
    as the CERT and the CIAC. (See sections and
    Teams exists for many major government agencies and large
    corporations.  If such a team is available for your site, the
    notification of this team should be of primary importance during
    the early stages of an incident.  These teams are responsible for
    coordinating computer security incidents over a range of sites and
    larger entities.  Even if the incident is believed to be contained
    to a single site, it is possible that the information available
    through a response team could help in closing out the incident.
    In setting up a site policy for incident handling, it may be
    desirable to create an incident handling team (IHT), much like
    those teams that already exist, that will be responsible for
    handling computer security incidents for the site (or
    organization).  If such a team is created, it is essential that
    communication lines be opened between this team and other IHTs.
    Once an incident is under way, it is difficult to open a trusted

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    dialogue between other IHTs if none has existed before.

5.4 Response

 A major topic still untouched here is how to actually respond to an
 event.  The response to an event will fall into the general
 categories of containment, eradication, recovery, and follow-up.
    The purpose of containment is to limit the extent of an attack.
    For example, it is important to limit the spread of a worm attack
    on a network as quickly as possible.  An essential part of
    containment is decision making (i.e., determining whether to shut
    a system down, to disconnect from a network, to monitor system or
    network activity, to set traps, to disable functions such as
    remote file transfer on a UNIX system, etc.).  Sometimes this
    decision is trivial; shut the system down if the system is
    classified or sensitive, or if proprietary information is at risk!
    In other cases, it is worthwhile to risk having some damage to the
    system if keeping the system up might enable you to identify an
    The third stage, containment, should involve carrying out
    predetermined procedures.  Your organization or site should, for
    example, define acceptable risks in dealing with an incident, and
    should prescribe specific actions and strategies accordingly.
    Finally, notification of cognizant authorities should occur during
    this stage.
    Once an incident has been detected, it is important to first think
    about containing the incident.  Once the incident has been
    contained, it is now time to eradicate the cause.  Software may be
    available to help you in this effort.  For example, eradication
    software is available to eliminate most viruses which infect small
    systems.  If any bogus files have been created, it is time to
    delete them at this point.  In the case of virus infections, it is
    important to clean and reformat any disks containing infected
    files.  Finally, ensure that all backups are clean.  Many systems
    infected with viruses become periodically reinfected simply
    because people do not systematically eradicate the virus from
    Once the cause of an incident has been eradicated, the recovery

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    phase defines the next stage of action.  The goal of recovery is
    to return the system to normal.  In the case of a network-based
    attack, it is important to install patches for any operating
    system vulnerability which was exploited.
    One of the most important stages of responding to incidents is
    also the most often omitted---the follow-up stage.  This stage is
    important because it helps those involved in handling the incident
    develop a set of "lessons learned" (see section 6.3) to improve
    future performance in such situations.  This stage also provides
    information which justifies an organization's computer security
    effort to management, and yields information which may be
    essential in legal proceedings.
    The most important element of the follow-up stage is performing a
    postmortem analysis.  Exactly what happened, and at what times?
    How well did the staff involved with the incident perform?  What
    kind of information did the staff need quickly, and how could they
    have gotten that information as soon as possible?  What would the
    staff do differently next time?  A follow-up report is valuable
    because it provides a reference to be used in case of other
    similar incidents.  Creating a formal chronology of events
    (including time stamps) is also important for legal reasons.
    Similarly, it is also important to as quickly obtain a monetary
    estimate of the amount of damage the incident caused in terms of
    any loss of software and files, hardware damage, and manpower
    costs to restore altered files, reconfigure affected systems, and
    so forth.  This estimate may become the basis for subsequent
    prosecution activity by the FBI, the U.S. Attorney General's
    Office, etc..
 5.4.1  What Will You Do?
    o Restore control.
    o Relation to policy.
    o Which level of service is needed?
    o Monitor activity.
    o Constrain or shut down system.
 5.4.2  Consider Designating a "Single Point of Contact"
    When an incident is under way, a major issue is deciding who is in
    charge of coordinating the activity of the multitude of players.
    A major mistake that can be made is to have a number of "points of
    contact" (POC) that are not pulling their efforts together.  This
    will only add to the confusion of the event, and will probably

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    lead to additional confusion and wasted or ineffective effort.
    The single point of contact may or may not be the person "in
    charge" of the incident.  There are two distinct rolls to fill
    when deciding who shall be the point of contact and the person in
    charge of the incident.  The person in charge will make decisions
    as to the interpretation of policy applied to the event.  The
    responsibility for the handling of the event falls onto this
    person.  In contrast, the point of contact must coordinate the
    effort of all the parties involved with handling the event.
    The point of contact must be a person with the technical expertise
    to successfully coordinate the effort of the system managers and
    users involved in monitoring and reacting to the attack.  Often
    the management structure of a site is such that the administrator
    of a set of resources is not a technically competent person with
    regard to handling the details of the operations of the computers,
    but is ultimately responsible for the use of these resources.
    Another important function of the POC is to maintain contact with
    law enforcement and other external agencies (such as the CIA, DoD,
    U.S.  Army, or others) to assure that multi-agency involvement
    Finally, if legal action in the form of prosecution is involved,
    the POC may be able to speak for the site in court.  The
    alternative is to have multiple witnesses that will be hard to
    coordinate in a legal sense, and will weaken any case against the
    attackers.  A single POC may also be the single person in charge
    of evidence collected, which will keep the number of people
    accounting for evidence to a minimum.  As a rule of thumb, the
    more people that touch a potential piece of evidence, the greater
    the possibility that it will be inadmissible in court.  The
    section below (Legal/Investigative) will provide more details for
    consideration on this topic.

5.5 Legal/Investigative

 5.5.1  Establishing Contacts with Investigative Agencies
    It is important to establish contacts with personnel from
    investigative agencies such as the FBI and Secret Service as soon
    as possible, for several reasons.  Local law enforcement and local
    security offices or campus police organizations should also be
    informed when appropriate.  A primary reason is that once a major
    attack is in progress, there is little time to call various
    personnel in these agencies to determine exactly who the correct
    point of contact is.  Another reason is that it is important to

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    cooperate with these agencies in a manner that will foster a good
    working relationship, and that will be in accordance with the
    working procedures of these agencies.  Knowing the working
    procedures in advance and the expectations of your point of
    contact is a big step in this direction.  For example, it is
    important to gather evidence that will be admissible in a court of
    law.  If you don't know in advance how to gather admissible
    evidence, your efforts to collect evidence during an incident are
    likely to be of no value to the investigative agency with which
    you deal.  A final reason for establishing contacts as soon as
    possible is that it is impossible to know the particular agency
    that will assume jurisdiction in any given incident.  Making
    contacts and finding the proper channels early will make
    responding to an incident go considerably more smoothly.
    If your organization or site has a legal counsel, you need to
    notify this office soon after you learn that an incident is in
    progress.  At a minimum, your legal counsel needs to be involved
    to protect the legal and financial interests of your site or
    organization.  There are many legal and practical issues, a few of
    which are:
       1. Whether your site or organization is willing to risk
          negative publicity or exposure to cooperate with legal
          prosecution efforts.
       2. Downstream liability--if you leave a compromised system
          as is so it can be monitored and another computer is damaged
          because the attack originated from your system, your site or
          organization may be liable for damages incurred.
       3. Distribution of information--if your site or organization
          distributes information about an attack in which another
          site or organization may be involved or the vulnerability
          in a product that may affect ability to market that
          product, your site or organization may again be liable
          for any damages (including damage of reputation).
       4. Liabilities due to monitoring--your site or organization
          may be sued if users at your site or elsewhere discover
          that your site is monitoring account activity without
          informing users.
    Unfortunately, there are no clear precedents yet on the
    liabilities or responsibilities of organizations involved in a
    security incident or who might be involved in supporting an
    investigative effort.  Investigators will often encourage
    organizations to help trace and monitor intruders -- indeed, most

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    investigators cannot pursue computer intrusions without extensive
    support from the organizations involved.  However, investigators
    cannot provide protection from liability claims, and these kinds
    of efforts may drag out for months and may take lots of effort.
    On the other side, an organization's legal council may advise
    extreme caution and suggest that tracing activities be halted and
    an intruder shut out of the system.  This in itself may not
    provide protection from liability, and may prevent investigators
    from identifying anyone.
    The balance between supporting investigative activity and limiting
    liability is tricky; you'll need to consider the advice of your
    council and the damage the intruder is causing (if any) in making
    your decision about what to do during any particular incident.
    Your legal counsel should also be involved in any decision to
    contact investigative agencies when an incident occurs at your
    site.  The decision to coordinate efforts with investigative
    agencies is most properly that of your site or organization.
    Involving your legal counsel will also foster the multi-level
    coordination between your site and the particular investigative
    agency involved which in turn results in an efficient division of
    labor.  Another result is that you are likely to obtain guidance
    that will help you avoid future legal mistakes.
    Finally, your legal counsel should evaluate your site's written
    procedures for responding to incidents.  It is essential to obtain
    a "clean bill of health" from a legal perspective before you
    actually carry out these procedures.
 5.5.2  Formal and Informal Legal Procedures
    One of the most important considerations in dealing with
    investigative agencies is verifying that the person who calls
    asking for information is a legitimate representative from the
    agency in question.  Unfortunately, many well intentioned people
    have unknowingly leaked sensitive information about incidents,
    allowed unauthorized people into their systems, etc., because a
    caller has masqueraded as an FBI or Secret Service agent.  A
    similar consideration is using a secure means of communication.
    Because many network attackers can easily reroute electronic mail,
    avoid using electronic mail to communicate with other agencies (as
    well as others dealing with the incident at hand).  Non-secured
    phone lines (e.g., the phones normally used in the business world)
    are also frequent targets for tapping by network intruders, so be

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    There is no established set of rules for responding to an incident
    when the U.S. Federal Government becomes involved.  Except by
    court order, no agency can force you to monitor, to disconnect
    from the network, to avoid telephone contact with the suspected
    attackers, etc..  As discussed in section 5.5.1, you should
    consult the matter with your legal counsel, especially before
    taking an action that your organization has never taken.  The
    particular agency involved may ask you to leave an attacked
    machine on and to monitor activity on this machine, for example.
    Your complying with this request will ensure continued cooperation
    of the agency--usually the best route towards finding the source
    of the network attacks and, ultimately, terminating these attacks.
    Additionally, you may need some information or a favor from the
    agency involved in the incident.  You are likely to get what you
    need only if you have been cooperative.  Of particular importance
    is avoiding unnecessary or unauthorized disclosure of information
    about the incident, including any information furnished by the
    agency involved.  The trust between your site and the agency
    hinges upon your ability to avoid compromising the case the agency
    will build; keeping "tight lipped" is imperative.
    Sometimes your needs and the needs of an investigative agency will
    differ.  Your site may want to get back to normal business by
    closing an attack route, but the investigative agency may want you
    to keep this route open.  Similarly, your site may want to close a
    compromised system down to avoid the possibility of negative
    publicity, but again the investigative agency may want you to
    continue monitoring.  When there is such a conflict, there may be
    a complex set of tradeoffs (e.g., interests of your site's
    management, amount of resources you can devote to the problem,
    jurisdictional boundaries, etc.).  An important guiding principle
    is related to what might be called "Internet citizenship" [22,
    IAB89, 23] and its responsibilities.  Your site can shut a system
    down, and this will relieve you of the stress, resource demands,
    and danger of negative exposure.  The attacker, however, is likely
    to simply move on to another system, temporarily leaving others
    blind to the attacker's intention and actions until another path
    of attack can be detected.  Providing that there is no damage to
    your systems and others, the most responsible course of action is
    to cooperate with the participating agency by leaving your
    compromised system on.  This will allow monitoring (and,
    ultimately, the possibility of terminating the source of the
    threat to systems just like yours).  On the other hand, if there
    is damage to computers illegally accessed through your system, the
    choice is more complicated: shutting down the intruder may prevent
    further damage to systems, but might make it impossible to track
    down the intruder.  If there has been damage, the decision about
    whether it is important to leave systems up to catch the intruder

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    should involve all the organizations effected.  Further
    complicating the issue of network responsibility is the
    consideration that if you do not cooperate with the agency
    involved, you will be less likely to receive help from that agency
    in the future.

5.6 Documentation Logs

 When you respond to an incident, document all details related to the
 incident.  This will provide valuable information to yourself and
 others as you try to unravel the course of events.  Documenting all
 details will ultimately save you time.  If you don't document every
 relevant phone call, for example, you are likely to forget a good
 portion of information you obtain, requiring you to contact the
 source of information once again.  This wastes yours and others'
 time, something you can ill afford.  At the same time, recording
 details will provide evidence for prosecution efforts, providing the
 case moves in this direction.  Documenting an incident also will help
 you perform a final assessment of damage (something your management
 as well as law enforcement officers will want to know), and will
 provide the basis for a follow-up analysis in which you can engage in
 a valuable "lessons learned" exercise.
 During the initial stages of an incident, it is often infeasible to
 determine whether prosecution is viable, so you should document as if
 you are gathering evidence for a court case.  At a minimum, you
 should record:
    o All system events (audit records).
    o All actions you take (time tagged).
    o All phone conversations (including the person with whom
      you talked, the date and time, and the content of the
 The most straightforward way to maintain documentation is keeping a
 log book.  This allows you to go to a centralized, chronological
 source of information when you need it, instead of requiring you to
 page through individual sheets of paper.  Much of this information is
 potential evidence in a court of law.  Thus, when you initially
 suspect that an incident will result in prosecution or when an
 investigative agency becomes involved, you need to regularly (e.g.,
 every day) turn in photocopied, signed copies of your logbook (as
 well as media you use to record system events) to a document
 custodian who can store these copied pages in a secure place (e.g., a
 safe).  When you submit information for storage, you should in return
 receive a signed, dated receipt from the document custodian.  Failure
 to observe these procedures can result in invalidation of any
 evidence you obtain in a court of law.

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6. Establishing Post-Incident Procedures

6.1 Overview

 In the wake of an incident, several actions should take place.  These
 actions can be summarized as follows:
    1. An inventory should be taken of the systems' assets,
       i.e., a careful examination should determine how the
       system was affected by the incident,
    2. The lessons learned as a result of the incident
       should be included in revised security plan to
       prevent the incident from re-occurring,
    3. A new risk analysis should be developed in light of the
    4. An investigation and prosecution of the individuals
       who caused the incident should commence, if it is
       deemed desirable.
 All four steps should provide feedback to the site security policy
 committee, leading to prompt re-evaluation and amendment of the
 current policy.

6.2 Removing Vulnerabilities

 Removing all vulnerabilities once an incident has occurred is
 difficult.  The key to removing vulnerabilities is knowledge and
 understanding of the breach.  In some cases, it is prudent to remove
 all access or functionality as soon as possible, and then restore
 normal operation in limited stages.  Bear in mind that removing all
 access while an incident is in progress will obviously notify all
 users, including the alleged problem users, that the administrators
 are aware of a problem; this may have a deleterious effect on an
 investigation.  However, allowing an incident to continue may also
 open the likelihood of greater damage, loss, aggravation, or
 liability (civil or criminal).
 If it is determined that the breach occurred due to a flaw in the
 systems' hardware or software, the vendor (or supplier) and the CERT
 should be notified as soon as possible.  Including relevant telephone
 numbers (also electronic mail addresses and fax numbers) in the site
 security policy is strongly recommended.  To aid prompt
 acknowledgment and understanding of the problem, the flaw should be
 described in as much detail as possible, including details about how
 to exploit the flaw.

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 As soon as the breach has occurred, the entire system and all its
 components should be considered suspect.  System software is the most
 probable target.  Preparation is key to recovering from a possibly
 tainted system.  This includes checksumming all tapes from the vendor
 using a checksum algorithm which (hopefully) is resistant to
 tampering [10].  (See sections,  Assuming original
 vendor distribution tapes are available, an analysis of all system
 files should commence, and any irregularities should be noted and
 referred to all parties involved in handling the incident.  It can be
 very difficult, in some cases, to decide which backup tapes to
 recover from; consider that the incident may have continued for
 months or years before discovery, and that the suspect may be an
 employee of the site, or otherwise have intimate knowledge or access
 to the systems.  In all cases, the pre-incident preparation will
 determine what recovery is possible.  At worst-case, restoration from
 the original manufactures' media and a re-installation of the systems
 will be the most prudent solution.
 Review the lessons learned from the incident and always update the
 policy and procedures to reflect changes necessitated by the
 6.2.1  Assessing Damage
    Before cleanup can begin, the actual system damage must be
    discerned.  This can be quite time consuming, but should lead into
    some of the insight as to the nature of the incident, and aid
    investigation and prosecution.  It is best to compare previous
    backups or original tapes when possible; advance preparation is
    the key.  If the system supports centralized logging (most do), go
    back over the logs and look for abnormalities.  If process
    accounting and connect time accounting is enabled, look for
    patterns of system usage.  To a lesser extent, disk usage may shed
    light on the incident.  Accounting can provide much helpful
    information in an analysis of an incident and subsequent
 6.2.2  Cleanup
    Once the damage has been assessed, it is necessary to develop a
    plan for system cleanup.  In general, bringing up services in the
    order of demand to allow a minimum of user inconvenience is the
    best practice.  Understand that the proper recovery procedures for
    the system are extremely important and should be specific to the
    It may be necessary to go back to the original distributed tapes
    and recustomize the system.  To facilitate this worst case

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    scenario, a record of the original systems setup and each
    customization change should be kept current with each change to
    the system.
 6.2.3  Follow up
    Once you believe that a system has been restored to a "safe"
    state, it is still possible that holes and even traps could be
    lurking in the system.  In the follow-up stage, the system should
    be monitored for items that may have been missed during the
    cleanup stage.  It would be prudent to utilize some of the tools
    mentioned in section (e.g., COPS) as a start.  Remember,
    these tools don't replace continual system monitoring and good
    systems administration procedures.
 6.2.4  Keep a Security Log
    As discussed in section 5.6, a security log can be most valuable
    during this phase of removing vulnerabilities.  There are two
    considerations here; the first is to keep logs of the procedures
    that have been used to make the system secure again.  This should
    include command procedures (e.g., shell scripts) that can be run
    on a periodic basis to recheck the security.  Second, keep logs of
    important system events.  These can be referenced when trying to
    determine the extent of the damage of a given incident.

6.3 Capturing Lessons Learned

 6.3.1  Understand the Lesson
    After an incident, it is prudent to write a report describing the
    incident, method of discovery, correction procedure, monitoring
    procedure, and a summary of lesson learned.  This will aid in the
    clear understanding of the problem.  Remember, it is difficult to
    learn from an incident if you don't understand the source.
 6.3.2  Resources  Other Security Devices, Methods
       Security is a dynamic, not static process.  Sites are dependent
       on the nature of security available at each site, and the array
       of devices and methods that will help promote security.
       Keeping up with the security area of the computer industry and
       their methods will assure a security manager of taking
       advantage of the latest technology.

Site Security Policy Handbook Working Group [Page 80] RFC 1244 Site Security Handbook July 1991  Repository of Books, Lists, Information Sources
       Keep an on site collection of books, lists, information
       sources, etc., as guides and references for securing the
       system.  Keep this collection up to date.  Remember, as systems
       change, so do security methods and problems.  Form a Subgroup
       Form a subgroup of system administration personnel that will be
       the core security staff.  This will allow discussions of
       security problems and multiple views of the site's security
       issues.  This subgroup can also act to develop the site
       security policy and make suggested changes as necessary to
       ensure site security.

6.4 Upgrading Policies and Procedures

 6.4.1  Establish Mechanisms for Updating Policies, Procedures,
        and Tools
    If an incident is based on poor policy, and unless the policy is
    changed, then one is doomed to repeat the past.  Once a site has
    recovered from and incident, site policy and procedures should be
    reviewed to encompass changes to prevent similar incidents.  Even
    without an incident, it would be prudent to review policies and
    procedures on a regular basis.  Reviews are imperative due to
    today's changing computing environments.
 6.4.2  Problem Reporting Procedures
    A problem reporting procedure should be implemented to describe,
    in detail, the incident and the solutions to the incident.  Each
    incident should be reviewed by the site security subgroup to allow
    understanding of the incident with possible suggestions to the
    site policy and procedures.

7. References

 [1] Quarterman, J., "The Matrix: Computer Networks and Conferencing
     Systems Worldwide", Pg. 278, Digital Press, Bedford, MA, 1990.
 [2] Brand, R., "Coping with the Threat of Computer Security
     Incidents: A Primer from Prevention through Recovery", R. Brand,
     available on-line from:, 8 June
 [3] Fites, M., Kratz, P. and A. Brebner, "Control and Security of

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     Computer Information Systems", Computer Science Press, 1989.
 [4] Johnson, D., and J. Podesta, "Formulating a Company Policy on
     Access to and Use and Disclosure of Electronic Mail on Company
     Computer Systems", Available from: The Electronic Mail
     Association (EMA) 1555 Wilson Blvd, Suite 555, Arlington VA
     22209, (703) 522-7111, 22 October 1990.
 [5] Curry, D., "Improving the Security of Your UNIX System", SRI
     International Report ITSTD-721-FR-90-21, April 1990.
 [6] Cheswick, B., "The Design of a Secure Internet Gateway",
     Proceedings of the Summer Usenix Conference, Anaheim, CA, June
 [7] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
     I -- Message Encipherment and Authentication Procedures", RFC
     1113, IAB Privacy Task Force, August 1989.
 [8] Kent, S., and J. Linn, "Privacy Enhancement for Internet
     Electronic Mail: Part II -- Certificate-Based Key Management",
     RFC 1114, IAB Privacy Task Force, August 1989.
 [9] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
     III -- Algorithms, Modes, and Identifiers", RFC 1115, IAB Privacy
     Task Force, August 1989.
[10] Merkle, R., "A Fast Software One Way Hash Function", Journal of
     Cryptology, Vol. 3, No. 1.
[11] Postel, J., "Internet Protocol - DARPA Internet Program Protocol
     Specification", RFC 791, DARPA, September 1981.
[12] Postel, J., "Transmission Control Protocol - DARPA Internet
     Program Protocol Specification", RFC 793, DARPA, September 1981.
[13] Postel, J., "User Datagram Protocol", RFC 768, USC/Information
     Sciences Institute, 28 August 1980.
[14] Mogul, J., "Simple and Flexible Datagram Access Controls for
     UNIX-based Gateways", Digital Western Research Laboratory
     Research Report 89/4, March 1989.
[15] Bellovin, S., and M. Merritt, "Limitations of the Kerberos
     Authentication System", Computer Communications Review, October
[16] Pfleeger, C., "Security in Computing", Prentice-Hall, Englewood

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     Cliffs, N.J., 1989.
[17] Parker, D., Swope, S., and B. Baker, "Ethical Conflicts:
     Information and Computer Science, Technology and Business", QED
     Information Sciences, Inc., Wellesley, MA.
[18] Forester, T., and P. Morrison, "Computer Ethics: Tales and
     Ethical Dilemmas in Computing", MIT Press, Cambridge, MA, 1990.
[19] Postel, J., and J. Reynolds, "Telnet Protocol Specification", RFC
     854, USC/Information Sciences Institute, May 1983.
[20] Postel, J., and J. Reynolds, "File Transfer Protocol", RFC 959,
     USC/Information Sciences Institute, October 1985.
[21] Postel, J., Editor, "IAB Official Protocol Standards", RFC 1200,
     IAB, April 1991.
[22] Internet Activities Board, "Ethics and the Internet", RFC 1087,
     Internet Activities Board, January 1989.
[23] Pethia, R., Crocker, S., and B. Fraser, "Policy Guidelines for
     the Secure Operation of the Internet", CERT, TIS, CERT, RFC in
[24] Computer Emergency Response Team (CERT/CC), "Unauthorized
     Password Change Requests", CERT Advisory CA-91:03, April 1991.
[25] Computer Emergency Response Team (CERT/CC), "TELNET Breakin
     Warning", CERT Advisory CA-89:03, August 1989.
[26] CCITT, Recommendation X.509, "The Directory: Authentication
     Framework", Annex C.
[27] Farmer, D., and E. Spafford, "The COPS Security Checker System",
     Proceedings of the Summer 1990 USENIX Conference, Anaheim, CA,
     Pgs. 165-170, June 1990.

8. Annotated Bibliography

 The intent of this annotated bibliography is to offer a
 representative collection of resources of information that will help
 the user of this handbook.  It is meant provide a starting point for
 further research in the security area.  Included are references to
 other sources of information for those who wish to pursue issues of
 the computer security environment.

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8.1 Computer Law

         American Bar Association, Section of Science and
         Technology, "Guide to the Prosecution of Telecommunication
         Fraud by the Use of Computer Crime Statutes", American Bar
         Association, 1989.
         Bender, D., "Computer Law: Evidence and Procedure",
         M. Bender, New York, NY, 1978-present.
         Kept up to date with supplements.
         Years covering 1978-1984 focuses on: Computer law,
         evidence and procedures.  The years 1984 to the current
         focus on general computer law.  Bibliographical
         references and index included.
         Bloombecker, B., "Spectacular Computer Crimes", Dow Jones-
         Irwin, Homewood, IL. 1990.
         Commerce Clearing House, "Guide to Computer Law", (Topical
         Law Reports), Chicago, IL., 1989.
         Court cases and decisions rendered by federal and state
         courts throughout the United States on federal and state
         computer law.  Includes Case Table and Topical Index.
         Conly, C., "Organizing for Computer Crime Investigation and
         Prosecution", U.S. Dept. of Justice, Office of Justice
         Programs, Under Contract  Number OJP-86-C-002, National
         Institute of Justice, Washington, DC, July 1989.
         Fenwick, W., Chair, "Computer Litigation, 1985: Trial
         Tactics and Techniques", Litigation Course Handbook
         Series No. 280, Prepared for distribution at the
         Computer Litigation, 1985: Trial Tactics and
         Techniques Program, February-March 1985.
         Gemignani, M., "Viruses and Criminal Law", Communications
         of the ACM, Vol. 32, No. 6, Pgs. 669-671, June 1989.

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         Huband, F., and R. Shelton, Editors, "Protection of
         Computer Systems and Software: New Approaches for Combating
         Theft of Software and Unauthorized Intrusion", Papers
         presented at a workshop sponsored by the National Science
         Foundation, 1986.
         McEwen, J., "Dedicated Computer Crime Units", Report
         Contributors: D. Fester and H. Nugent, Prepared for the
         National Institute of Justice, U.S. Department of Justice,
         by Institute for Law and Justice, Inc., under contract number
         OJP-85-C-006, Washington, DC, 1989.
         Parker, D., "Computer Crime: Criminal Justice Resource
         Manual", U.S. Dept. of Justice, National Institute of Justice,
         Office of Justice Programs, Under Contract Number
         OJP-86-C-002, Washington, D.C., August 1989.
         Shaw, E., Jr., "Computer Fraud and Abuse Act of 1986,
         Congressional Record (3 June 1986), Washington, D.C.,
         3 June 1986.
         Trible, P., "The Computer Fraud and Abuse Act of 1986",
         U.S. Senate Committee on the Judiciary, 1986.

8.2 Computer Security

         Caelli, W., Editor, "Computer Security in the Age of
         Information", Proceedings of the Fifth IFIP International
         Conference on Computer Security, IFIP/Sec '88.
         Carroll, J., "Computer Security", 2nd Edition, Butterworth
         Publishers, Stoneham, MA, 1987.
         Cooper, J., "Computer and Communications Security:
         Strategies for the 1990s", McGraw-Hill, 1989.
         Brand, R., "Coping with the Threat of Computer Security
         Incidents: A Primer from Prevention through Recovery",

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         R. Brand, 8 June 1990.
         As computer security becomes a more important issue in
         modern society, it begins to warrant a systematic approach.
         The vast majority of the computer security problems and the
         costs associated with them can be prevented with simple
         inexpensive measures.  The most important and cost
         effective of these measures are available in the prevention
         and planning phases.  These methods are presented in this
         paper, followed by a simplified guide to incident
         handling and recovery.  Available on-line from:
         Cheswick, B., "The Design of a Secure Internet Gateway",
         Proceedings of the Summer Usenix Conference, Anaheim, CA,
         June 1990.
         Brief abstract (slight paraphrase from the original
         abstract): AT&T maintains a large internal Internet that
         needs to be protected from outside attacks, while
         providing useful services between the two.
         This paper describes AT&T's Internet gateway.  This
         gateway passes mail and many of the common Internet
         services between AT&T internal machines and the Internet.
         This is accomplished without IP connectivity using a pair
         of machines: a trusted internal machine and an untrusted
         external gateway.  These are connected by a private link.
         The internal machine provides a few carefully-guarded
         services to the external gateway.  This configuration
         helps protect the internal internet even if the external
         machine is fully compromised.
         This is a very useful and interesting design.  Most
         firewall gateway systems rely on a system that, if
         compromised, could allow access to the machines behind
         the firewall.  Also, most firewall systems require users
         who want access to Internet services to have accounts on
         the firewall machine.  AT&T's design allows AT&T internal
         internet users access to the standard services of TELNET and
         FTP from their own workstations without accounts on
         the firewall machine.  A very useful paper that shows
         how to maintain some of the benefits of Internet
         connectivity while still maintaining strong

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         Curry, D., "Improving the Security of Your UNIX System",
         SRI International Report ITSTD-721-FR-90-21, April 1990.
         This paper describes measures that you, as a system
         administrator can take to make your UNIX system(s) more
         secure.  Oriented primarily at SunOS 4.x, most of the
         information covered applies equally well to any Berkeley
         UNIX system with or without NFS and/or Yellow Pages (NIS).
         Some of the information can also be applied to System V,
         although this is not a primary focus of the paper.  A very
         useful reference, this is also available on the Internet in
         various locations, including the directory
         Fites, M., Kratz, P. and A. Brebner, "Control and
         Security of Computer Information Systems", Computer Science
         Press, 1989.
         This book serves as a good guide to the issues encountered
         in forming computer security policies and procedures.  The
         book is designed as a textbook for an introductory course
         in information systems security.
         The book is divided into five sections: Risk Management (I),
         Safeguards: security and control measures, organizational
         and administrative (II), Safeguards: Security and Control
         Measures, Technical (III), Legal Environment and
         Professionalism (IV), and CICA Computer Control Guidelines
         The book is particularly notable for its straight-forward
         approach to security, emphasizing that common sense is the
         first consideration in designing a security program.  The
         authors note that there is a tendency to look to more
         technical solutions to security problems while overlooking
         organizational controls which are often cheaper and much
         more effective.  298 pages, including references and index.
         Garfinkel, S, and E. Spafford, "Practical Unix Security",
         O'Reilly & Associates, ISBN 0-937175-72-2, May 1991.
         Approx 450 pages, $29.95.  Orders: 1-800-338-6887
         (US & Canada), 1-707-829-0515 (Europe), email:
         This is one of the most useful books available on Unix

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         security.  The first part of the book covers standard Unix
         and Unix security basics, with particular emphasis on
         passwords.  The second section covers enforcing security on
         the system.  Of particular interest to the Internet user are
         the sections on network security, which address many
         of the common security problems that afflict Internet Unix
         users.  Four chapters deal with handling security incidents,
         and the book concludes with discussions of encryption,
         physical security, and useful checklists and lists of
         resources.  The book lives up to its name; it is filled with
         specific references to possible security holes, files to
         check, and things to do to improve security.  This
         book is an excellent complement to this handbook.
         Greenia, M., "Computer Security Information Sourcebook",
         Lexikon Services, Sacramento, CA, 1989.
         A manager's guide to computer security.  Contains a
         sourcebook of key reference materials including
         access control and computer crimes bibliographies.
         Hoffman, L., "Rogue Programs: Viruses, Worms, and
         Trojan Horses", Van Nostrand Reinhold, NY, 1990.
         (384 pages, includes bibliographical references and index.)
         Johnson, D., and J. Podesta, "Formulating A Company Policy
         on Access to and Use and Disclosure of Electronic Mail on
         Company Computer Systems".
         A white paper prepared for the EMA, written by two experts
         in privacy law.  Gives background on the issues, and presents
         some policy options.
         Available from: The Electronic Mail Association (EMA)
         1555 Wilson Blvd, Suite 555, Arlington, VA, 22209.
         (703) 522-7111.
         Kent, Stephen, "E-Mail Privacy for the Internet: New Software
         and Strict Registration Procedures will be Implemented this
         Year", Business Communications Review, Vol. 20, No. 1,
         Pg. 55, 1 January 1990.

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         Lu, W., and M. Sundareshan, "Secure Communication in
         Internet Environments: A Hierachical Key Management Scheme
         for End-to-End Encryption", IEEE Transactions on
         Communications, Vol. 37, No. 10, Pg. 1014, 1 October 1989.
         Lu, W., and M. Sundareshan, "A Model for Multilevel Security
         in Computer Networks", IEEE Transactions on Software
         Engineering, Vol. 16, No. 6, Page 647, 1 June 1990.
         National Security Agency, "Information Systems Security
         Products and Services Catalog", NSA, Quarterly Publication.
         NSA's catalogue contains chapter on: Endorsed Cryptographic
         Products List; NSA Endorsed Data Encryption Standard (DES)
         Products List; Protected Services List; Evaluated Products
         List; Preferred Products List; and Endorsed Tools List.
         The catalogue is available from the Superintendent of
         Documents, U.S. Government Printing Office, Washington,
         D.C.  One may place telephone orders by calling:
         (202) 783-3238.
         United States Congress, Office of Technology Assessment,
         "Defending Secrets, Sharing Data: New Locks and Keys for
         Electronic Information", OTA-CIT-310, October 1987.
         This report, prepared for congressional committee considering
         Federal policy on the protection of electronic information, is
         interesting because of the issues it raises regarding the
         impact of technology used to protect information.  It also
         serves as a reasonable introduction to the various encryption
         and information protection mechanisms.  185 pages.  Available
         from the U.S. Government Printing Office.
         Palmer, I., and G. Potter, "Computer Security Risk
         Management", Van Nostrand Reinhold, NY, 1989.
         Pfleeger, C., "Security in Computing", Prentice-Hall,
         Englewood Cliffs, NJ, 1989.
         A general textbook in computer security, this book provides an
         excellent and very readable introduction to classic computer

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         security problems and solutions, with a particular emphasis on
         encryption.  The encryption coverage serves as a good
         introduction to the subject.  Other topics covered include
         building secure programs and systems, security of database,
         personal computer security, network and communications
         security, physical security, risk analysis and security
         planning, and legal and ethical issues.  538 pages including
         index and bibliography.
         Shirey, R., "Defense Data Network Security Architecture",
         Computer Communication Review, Vol. 20, No. 2, Page 66,
         1 April 1990.
         Spafford, E., Heaphy, K., and D. Ferbrache, "Computer
         Viruses: Dealing with Electronic Vandalism and Programmed
         Threats", ADAPSO, 1989. (109 pages.)
         This is a good general reference on computer viruses and
         related concerns.  In addition to describing viruses in
         some detail, it also covers more general security issues,
         legal recourse in case of security problems, and includes
         lists of laws, journals focused on computers security,
         and other security-related resources.
         Available from: ADAPSO, 1300 N. 17th St, Suite 300,
         Arlington VA 22209.  (703) 522-5055.
         Stoll, C., "Stalking the Wily Hacker", Communications
         of the ACM, Vol. 31, No. 5, Pgs. 484-497, ACM,
         New York, NY, May 1988.
         This article describes some of the technical means used
         to trace the intruder that was later chronicled in
         "Cuckoo's Egg" (see below).
         Stoll, C., "The Cuckoo's Egg", ISBN 00385-24946-2,
         Doubleday, 1989.
         Clifford Stoll, an astronomer turned UNIX System
         Administrator, recounts an exciting, true story of how he
         tracked a computer intruder through the maze of American
         military and research networks.  This book is easy to
         understand and can serve as an interesting introduction to
         the world of networking.  Jon Postel says in a book review,

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         "[this book] ... is absolutely essential reading for anyone
         that uses or operates any computer connected to the Internet
         or any other computer network."
         Vallabhaneni, S., "Auditing Computer Security: A Manual with
         Case Studies", Wiley, New York, NY, 1989.

8.3 Ethics

         Computer Professionals for Social Responsibility, "CPSR
         Statement on the Computer Virus", CPSR, Communications of the
         ACM, Vol. 32, No. 6, Pg. 699, June 1989.
         This memo is a statement on the Internet Computer Virus
         by the Computer Professionals for Social Responsibility
         Denning, Peter J., Editor, "Computers Under Attack:
         Intruders, Worms, and Viruses",  ACM Press, 1990.
         A collection of 40 pieces divided into six sections: the
         emergence of worldwide computer networks, electronic breakins,
         worms, viruses, counterculture (articles examining the world
         of the "hacker"), and finally a section discussing social,
         legal, and ethical considerations.
         A thoughtful collection that addresses the phenomenon of
         attacks on computers.  This includes a number of previously
         published articles and some new ones.  The previously
         published ones are well chosen, and include some references
         that might be otherwise hard to obtain.  This book is a key
         reference to computer security threats that have generated
         much of the concern over computer security in recent years.
         Ermann, D., Williams, M., and C. Gutierrez, Editors,
         "Computers, Ethics, and Society", Oxford University Press,
         NY, 1990.  (376 pages, includes bibliographical references).
         Forester, T., and P. Morrison, "Computer Ethics: Tales and
         Ethical Dilemmas in Computing", MIT Press, Cambridge, MA,
         1990.  (192 pages including index.)

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         From the preface: "The aim of this book is two-fold: (1) to
         describe some of the problems created by society by computers,
         and (2) to show how these problems present ethical dilemmas
         for computers professionals and computer users.
         The problems created by computers arise, in turn, from two
         main sources: from hardware and software malfunctions and
         from misuse by human beings.  We argue that computer systems
         by their very nature are insecure, unreliable, and
         unpredictable -- and that society has yet to come to terms
         with the consequences.  We also seek to show how society
         has become newly vulnerable to human misuse of computers in
         the form of computer crime, software theft, hacking, the
         creation of viruses, invasions of privacy, and so on."
         The eight chapters include "Computer Crime", "Software
         Theft", "Hacking and Viruses", "Unreliable Computers",
         "The Invasion of Privacy", "AI and Expert Systems",
         and "Computerizing the Workplace."  Includes extensive
         notes on sources and an index.
         Gould, C., Editor, "The Information Web: Ethical and Social
         Implications of Computer Networking", Westview Press,
         Boulder, CO, 1989.
         Internet Activities Board, "Ethics and the Internet",
         RFC 1087, IAB, January 1989.  Also appears in the
         Communications of the ACM, Vol. 32, No. 6, Pg. 710,
         June 1989.
         This memo is a statement of policy by the Internet
         Activities Board (IAB) concerning the proper use of
         the resources of the Internet.  Available on-line on
         host, directory rfc, filename rfc1087.txt.
         Also available on host, directory RFC,
         filename RFC1087.TXT-1.
         Martin, M., and R. Schinzinger, "Ethics in Engineering",
         McGraw Hill, 2nd Edition, 1989.
         Massachusetts Institute of Technology, "Teaching Students
         About Responsible Use of Computers", MIT, 1985-1986.  Also
         reprinted in the Communications of the ACM, Vol. 32, No. 6,
         Pg. 704, Athena Project, MIT, June 1989.

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         This memo is a statement of policy by the Massachusetts
         Institute of Technology (MIT) on the responsible use
         of computers.
         National Institute of Standards and Technology, "Computer
         Viruses and Related Threats: A Management Guide", NIST
         Special Publication 500-166, August 1989.
         National Science Foundation, "NSF Poses Code of Networking
         Ethics", Communications of the ACM, Vol. 32, No. 6, Pg. 688,
         June 1989.  Also appears in the minutes of the regular
         meeting of the Division Advisory Panel for Networking and
         Communications Research and Infrastructure, Dave Farber,
         Chair, November 29-30, 1988.
         This memo is a statement of policy by the National Science
         Foundation (NSF) concerning the ethical use of the Internet.
         Parker, D., Swope, S., and B. Baker, "Ethical Conflicts:
         Information and Computer Science, Technology and Business",
         QED Information Sciences, Inc., Wellesley, MA. (245 pages).
 Additional publications on Ethics:
 The University of New Mexico (UNM)
    The UNM has a collection of ethics documents.  Included are
    legislation from several states and policies from many
       Access is via FTP, IP address  Look in the
       directory /ethics.

8.4 The Internet Worm

         Brock, J., "November 1988 Internet Computer Virus and the
         Vulnerability of National Telecommunications Networks to
         Computer Viruses", GAO/T-IMTEC-89-10, Washington, DC,
         20 July 1989.
         Testimonial statement of Jack L. Brock, Director, U. S.
         Government Information before the Subcommittee on
         Telecommunications and Finance, Committee on Energy and

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         Commerce, House of Representatives.
         Eichin, M., and J. Rochlis, "With Microscope and Tweezers:
         An Analysis of the Internet Virus of November 1988",
         Massachusetts Institute of Technology, February 1989.
         Provides a detailed dissection of the worm program.  The
         paper discusses the major points of the worm program then
         reviews strategies, chronology, lessons and open issues,
         Acknowledgments; also included are a detailed appendix
         on the worm program subroutine by subroutine, an
         appendix on the cast of characters, and a reference section.
         Eisenberg, T., D. Gries, J. Hartmanis, D. Holcomb,
         M. Lynn, and T. Santoro, "The Computer Worm", Cornell
         University, 6 February 1989.
         A Cornell University Report presented to the Provost of the
         University on 6 February 1989 on the Internet Worm.
         U.S. General Accounting Office, "Computer Security - Virus
         Highlights Need for Improved Internet Management", United
         States General Accounting Office, Washington, DC, 1989.
         This 36 page report (GAO/IMTEC-89-57), by the U.S.
         Government Accounting Office, describes the Internet worm
         and its effects.  It gives a good overview of the various
         U.S. agencies involved in the Internet today and their
         concerns vis-a-vis computer security and networking.
         Available on-line on host, directory
         pub, filename GAO_RPT; and on, directory nsfnet,
         filename GAO_RPT.TXT.
         The Helminthiasis of the Internet, RFC 1135,
         USC/Information Sciences Institute, Marina del Rey,
         CA, December 1989.
         This report looks back at the helminthiasis (infestation
         with, or disease caused by parasitic worms) of the
         Internet that was unleashed the evening of 2 November 1988.
         This document provides a glimpse at the infection,its
         festering, and cure.  The impact of the worm on the Internet
         community, ethics statements, the role of the news media,

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         crime in the computer world, and future prevention is
         discussed.  A documentation review presents four publications
         that describe in detail this particular parasitic computer
         program.  Reference and bibliography sections are also
         included.  Available on-line on host
         directory rfc, filename rfc1135.txt.  Also available on
         host, directory RFC, filename RFC1135.TXT-1.
         Seeley, D., "A Tour of the Worm", Proceedings of 1989
         Winter USENIX Conference, Usenix Association, San Diego, CA,
         February 1989.
         Details are presented as a "walk thru" of this particular
         worm program.  The paper opened with an abstract,
         introduction, detailed chronology of events upon the
         discovery of the worm, an overview, the internals of the
         worm, personal opinions, and conclusion.
         Spafford, E., "The Internet Worm Program: An
         Analysis", Computer Communication Review, Vol. 19,
         No. 1, ACM SIGCOM, January 1989.  Also issued as Purdue
         CS Technical Report CSD-TR-823, 28 November 1988.
         Describes the infection of the Internet as a worm
         program that exploited flaws in utility programs in
         UNIX based systems.  The report gives a detailed
         description of the components of the worm program:
         data and functions.  Spafford focuses his study on two
         completely independent reverse-compilations of the
         worm and a version disassembled to VAX assembly language.
         Spafford, G., "An Analysis of the Internet Worm",
         Proceedings of the European Software Engineering
         Conference 1989, Warwick England, September 1989.
         Proceedings published by Springer-Verlag as: Lecture
         Notes in Computer Science #387.  Also issued
         as Purdue Technical Report #CSD-TR-933.

8.5 National Computer Security Center (NCSC)

 All NCSC publications, approved for public release, are available
 from the NCSC Superintendent of Documents.
         NCSC = National Computer Security Center

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         9800 Savage Road
         Ft Meade, MD 20755-6000
         CSC = Computer Security Center:
         an older name for the NCSC
         NTISS = National Telecommunications and
         Information Systems Security
         NTISS Committee, National Security Agency
         Ft Meade, MD 20755-6000
         Department of Defense, "Password Management Guideline",
         CSC-STD-002-85, 12 April 1985, 31 pages.
         The security provided by a password system depends on
         the passwords being kept secret at all times.  Thus, a
         password is vulnerable to compromise whenever it is used,
         stored, or even known.  In a password-based authentication
         mechanism implemented on an ADP system, passwords are
         vulnerable to compromise due to five essential aspects
         of the password system: 1) a password must be initially
         assigned to a user when enrolled on the ADP system;
         2) a user's password must be changed periodically;
         3) the ADP system must maintain a 'password
         database'; 4) users must remember their passwords; and
         5) users must enter their passwords into the ADP system at
         authentication time.  This guideline prescribes steps to be
         taken to minimize the vulnerability of passwords in each of
         these circumstances.
         NCSC, "A Guide to Understanding AUDIT in Trusted Systems",
         NCSC-TG-001, Version-2, 1 June 1988, 25 pages.
         Audit trails are used to detect and deter penetration of
         a computer system and to reveal usage that identifies
         misuse.  At the discretion of the auditor, audit trails
         may be limited to specific events or may encompass all of
         the activities on a system.  Although not required by
         the criteria, it should be possible for the target of the
         audit mechanism to be either a subject or an object.  That
         is to say, the audit mechanism should be capable of
         monitoring every time John accessed the system as well as
         every time the nuclear reactor file was accessed; and
         likewise every time John accessed the nuclear reactor

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         NCSC, "A Guide to Understanding DISCRETIONARY ACCESS CONTROL
         in Trusted Systems", NCSC-TG-003, Version-1, 30 September
         1987, 29 pages.
         Discretionary control is the most common type of access
         control mechanism implemented in computer systems today.
         The basis of this kind of security is that an individual
         user, or program operating on the user's behalf, is
         allowed to specify explicitly the types of access other
         users (or programs executing on their behalf) may have to
         information under the user's control.  [...]  Discretionary
         controls are not a replacement for mandatory controls.  In
         any environment in which information is protected,
         discretionary security provides for a finer granularity of
         control within the overall constraints of the mandatory
         NCSC, "A Guide to Understanding CONFIGURATION MANAGEMENT
         in Trusted Systems", NCSC-TG-006, Version-1, 28 March 1988,
         31 pages.
         Configuration management consists of four separate tasks:
         identification, control, status accounting, and auditing.
         For every change that is made to an automated data
         processing (ADP) system, the design and requirements of the
         changed version of the system should be identified.  The
         control task of configuration management is performed
         by subjecting every change to documentation, hardware, and
         software/firmware to review and approval by an authorized
         authority.  Configuration status accounting is responsible
         for recording and reporting on the configuration of the
         product throughout the change.  Finally, though the process
         of a configuration audit, the completed change can be
         verified to be functionally correct, and for trusted
         systems, consistent with the security policy of the system.
         NTISS, "Advisory Memorandum on Office Automation Security
         Guideline", NTISSAM CONPUSEC/1-87, 16 January 1987,
         58 pages.
         This document provides guidance to users, managers, security
         officers, and procurement officers of Office Automation
         Systems.  Areas addressed include: physical security,
         personnel security, procedural security, hardware/software
         security, emanations security (TEMPEST), and communications

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         security for stand-alone OA Systems, OA Systems
         used as terminals connected to mainframe computer systems,
         and OA Systems used as hosts in a Local Area Network (LAN).
         Differentiation is made between those Office Automation
         Systems equipped with removable storage media only (e.g.,
         floppy disks, cassette tapes, removable hard disks) and
         those Office Automation Systems equipped with fixed media
         (e.g., Winchester disks).

Additional NCSC Publications:

         National Computer Security Center, "Glossary of Computer
         Security Terms", NCSC-TG-004, NCSC, 21 October 1988.
         National Computer Security Center, "Trusted
         Computer System Evaluation Criteria", DoD 5200.28-STD,
         CSC-STD-001-83, NCSC, December 1985.
         National Computer Security Center, "Guidance for
         Applying the Department of Defense Trusted Computer System
         Evaluation Criteria in Specific Environments",
         CSC-STD-003-85, NCSC, 25 June 1985.
         National Computer Security Center, "Technical Rationale
         Behind CSC-STD-003-85: Computer Security Requirements",
         CSC-STD-004-85, NCSC, 25 June 85.
         National Computer Security Center, "Magnetic Remanence
         Security Guideline", CSC-STD-005-85, NCSC, 15 November 1985.
         This guideline is tagged as a "For Official Use Only"
         exemption under Section 6, Public Law 86-36 (50 U.S. Code
         402).  Distribution authorized of U.S. Government agencies
         and their contractors to protect unclassified technical,
         operational, or administrative data relating to operations
         of the National Security Agency.
         National Computer Security Center, "Guidelines for Formal
         Verification Systems", Shipping list no.: 89-660-P, The
         Center, Fort George G. Meade, MD, 1 April 1990.

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         National Computer Security Center, "Glossary of Computer
         Security Terms", Shipping list no.: 89-254-P, The Center,
         Fort George G. Meade, MD, 21 October 1988.
         National Computer Security Center, "Trusted UNIX Working
         Group (TRUSIX) rationale for selecting access control
         list features for the UNIX system", Shipping list no.:
         90-076-P, The Center, Fort George G. Meade, MD, 1990.
         National Computer Security Center, "Trusted Network
         Interpretation", NCSC-TG-005, NCSC, 31 July 1987.
         Tinto, M., "Computer Viruses: Prevention, Detection, and
         Treatment", National Computer Security Center C1
         Technical Report C1-001-89, June 1989.
         National Computer Security Conference, "12th National
         Computer Security Conference: Baltimore Convention Center,
         Baltimore, MD, 10-13 October, 1989: Information Systems
         Security, Solutions for Today - Concepts for Tomorrow",
         National Institute of Standards and National Computer
         Security Center, 1989.

8.6 Security Checklists

         Aucoin, R., "Computer Viruses: Checklist for Recovery",
         Computers in  Libraries, Vol. 9, No. 2, Pg. 4,
         1 February 1989.
         Wood, C., Banks, W., Guarro, S., Garcia, A., Hampel, V.,
         and H. Sartorio, "Computer Security:  A Comprehensive Controls
         Checklist", John Wiley and Sons, Interscience Publication,

8.7 Additional Publications

 Defense Data Network's Network Information Center (DDN NIC)
    The DDN NIC maintains DDN Security bulletins and DDN Management

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    bulletins online on the machine: NIC.DDN.MIL.  They are available
    via anonymous FTP.  The DDN Security bulletins are in the
    directory: SCC, and the DDN Management bulletins are in the
    directory: DDN-NEWS.
    For additional information, you may send a message to:
    NIC@NIC.DDN.MIL, or call the DDN NIC at: 1-800-235-3155.
         Defense Data Network, "BSD 4.2 and 4.3 Software Problem
         Resolution", DDN MGT Bulletin #43, DDN Network Information
         Center, 3 November 1988.
         A Defense Data Network Management Bulletin announcement
         on the 4.2bsd and 4.3bsd software fixes to the Internet
         DCA DDN Defense Communications System, "DDN Security
         Bulletin 03", DDN Security Coordination Center,
         17 October 1989.
 IEEE Proceedings
         "Proceedings of the IEEE Symposium on Security
         and Privacy", published annually.
    IEEE Proceedings are available from:
            Computer Society of the IEEE
            P.O. Box 80452
            Worldway Postal Center
            Los Angeles, CA  90080
 Other Publications:
    Computer Law and Tax Report
    Computers and Security
    Security Management Magazine
    Journal of Information Systems Management
    Data Processing & Communications Security
    SIG Security, Audit & Control Review

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9. Acknowledgments

 Thanks to the SSPHWG's illustrious "Outline Squad", who assembled at
 USC/Information Sciences Institute on 12-June-90: Ray Bates (ISI),
 Frank Byrum (DEC), Michael A. Contino (PSU), Dave Dalva (Trusted
 Information Systems, Inc.), Jim Duncan (Penn State Math Department),
 Bruce Hamilton (Xerox), Sean Kirkpatrick (Unisys), Tom Longstaff
 (CIAC/LLNL), Fred Ostapik (SRI/NIC), Keith Pilotti (SAIC), and Bjorn
 Satdeva (/sys/admin, inc.).
 Many thanks to Rich Pethia and the Computer Emergency Response Team
 (CERT); much of the work by Paul Holbrook was done while he was
 working for CERT.  Rich also provided a very thorough review of this
 document.  Thanks also to Jon Postel and USC/Information Sciences
 Institute for contributing facilities and moral support to this
 Last, but NOT least, we would like to thank members of the SSPHWG and
 Friends for their additional contributions: Vint Cerf (CNRI),
 Dave Grisham (UNM), Nancy Lee Kirkpatrick (Typist Extraordinaire),
 Chris McDonald (WSMR), H. Craig McKee (Mitre), Gene Spafford (Purdue),
 and Aileen Yuan (Mitre).

10. Security Considerations

 If security considerations had not been so widely ignored in the
 Internet, this memo would not have been possible.

11. Authors' Addresses

 J. Paul Holbrook
 CICNet, Inc.
 2901 Hubbard
 Ann Arbor, MI 48105
 Phone: (313) 998-7680
 Joyce K. Reynolds
 University of Southern California
 Information Sciences Institute
 4676 Admiralty Way
 Marina del Rey, CA 90292
 Phone: (213) 822-1511

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