TUCoPS :: Unix :: General :: ciacl128.txt

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 The U.S. Department of Energy
 Computer Incident Advisory Center
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 INFORMATION BULLETIN
 MIT Kerberos 5 telnetd Buffer Overflows
August 1, 2001 19:00 GMT Number L-128
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PROBLEM: A buffer overflow exists in telnetd. 
PLATFORM: MIT Kerberos 5, all releases to date. 
DAMAGE: An unauthorized remote user can gain root access. 
SOLUTION: Apply the appropriate patches and rebuild telnetd as prescribed 
 by MIT. 
______________________________________________________________________________
VULNERABILITY The risk is HIGH. The vulnerability has been discussed in open 
ASSESSMENT: forums. 
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LINKS: 
 CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/l-128.shtml 
 ORIGINAL BULLETIN: http://web.mit.edu/kerberos/www/advisories/telnetd.txt 
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[****** Start MIT Advisory ******]
		 KRB5 TELNETD BUFFER OVERFLOWS
2001年07月31日
SUMMARY:
Buffer overflows exist in the telnet daemon included with MIT krb5.
Exploits are believed to exist for various operating systems on at
least the i386 architecture.
IMPACT:
If telnetd is running, a remote user may gain unauthorized root
access.
VULNERABLE DISTRIBUTIONS:
* MIT Kerberos 5, all releases to date.
FIXES:
The recommended approach is to apply the appropriate patches and to
rebuild your telnetd. Patches for the krb5-1.2.2 release may be found
at:
	http://web.mit.edu/kerberos/www/advisories/telnetd_122_patch.txt
The associated detached PGP signature is at:
	http://web.mit.edu/kerberos/www/advisories/telnetd_122_patch.txt.asc
These patches might apply successfully to older releases with some
amount of fuzz.
Please note that if you are using GNU make to build your krb5 sources,
the build system may attempt to rebuild the configure script from the
changed configure.in. This may cause trouble if you don't have
autoconf installed properly. To prevent this, you should use the
touch command or some similar means to ensure that the file
modification time on the configure script is newer than that of the
configure.in file.
If you are unable to patch your telnetd, you may should disable the
telnet service altogether.
This announcement and code patches related to it may be found on the
MIT Kerberos security advisory page at:
	http://web.mit.edu/kerberos/www/advisories/index.html
The main MIT Kerberos web page is at:
	http://web.mit.edu/kerberos/www/index.html
ACKNOWLEDGMENTS:
Thanks to TESO for the original alert / Bugtraq posting.
Thanks to Jeffrey Altman for assistance in developing these patches.
DETAILS:
A buffer overflow bug was discovered in telnet daemons derived from
BSD source code. Since the telnet daemon in MIT krb5 uses code
largely derived originally from BSD sources, it too is vulnerable.
By carefully constructing a series of telnet options to send to a
telnet server, a remote attacker may exercise a bug relating to lack
of bounds-checking, causing an overflow of a fixed-size buffer. This
overflow may possibly force the execution of malicious code.
It is not known how difficult this vulnerability is to exploit, since
the buffer is not on the stack. Some discussion seems to indicate
that exploits exist for this vulnerability that are believed to work
against various operating systems for i386-based machines. It is not
known whether these existing exploits have been successfully ported to
other processors.
[****** End MIT Advisory ******]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of MIT for the 
information contained in this bulletin.
_______________________________________________________________________________
CIAC, the Computer Incident Advisory Center, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
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