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From: Fozzy [Hackademy Audit] (fozzy_at_dmpfrance.com)
Date: Tue Jan 28 2003 - 08:32:28 CST
--[ Description ]--
When retrieving a file on a remote server, if the filename begins with a
pipe character, the MIT Kerberos ftp client program (and possibly others)
will pass the filename as a command to the local shell in a system() call.
The standard input is the content of the file.
This should be an old known and fixed vulnerability on many ftp clients
(published in 1997 on the Bugtraq mailing list). However it seems it has
never been fixed in the MIT Kerberos utilities package.
--[ Impact ]--
Shell commands can be issued remotely on the machine of a user who is
retrieving files with this FTP client program, from a compromised or
malicious ftp server. This leads to compromise of the client machine.
For instance, some scripts use the ftp client to automaticaly collect and
archive files : the compromise of the server, or of any computer on the
local network that can do Man In the Middle attacks, leads to compromise of
any machine downloading the files using this ftp client.
RETR "|touch testfile"
RETR "|sh" with content of the file '|sh' being shell commands
--[ Disclosure Policy ]--
The Hackademy Audit team was surprised to find on December, 2002 that such
a simple and old known vulnerability was still lying around in current
software. So we thought that this issue might be a single distribution
packaging problem... but on the other hand it could also affect other ftp
clients, and could be present in many distribution and/or operating systems
implementing Kerberos (for instance, on some default installs of the Linux
Mandrake distribution, we found that the standard ftp client is a
vulnerable MIT Kerberos ftp). A quick glance at the international MIT
Kerberos source tree _seems_ to confirm that the problem is there.
We decided then to stop investigating this issue and give our informations
to the CERT, because they can make better investigation with different
vendors and responsible disclosure than we can. On Friday 24th January,
CERT published the Vulnerability Note VU#258721 about this issue, stating
that the MIT Kerberos client is actually vulnerable, and flagging many
vendors as having status "Unknown" or "Not vulnerable". No vendor have
provided a patch at this time. Please understand that this is the CERT
research and disclosure policy, not ours.
This advisory is only posted by us to different mailing-lists as a public
service, to attract attention of system administrators and vendors on the
VU#258721 CERT vulnerability note, because nobody else did. If something is
wrong, we are not the guys to blame ;-)
Please refer to the CERT web site for accurate and up-to-date information.
--[ Solution ]--
Due to the disclosure policy (see above), no patches are available at this
time. Anyway, consider this is a 1997 public vuln. And on a client program,
not a server.
[Note that the standard Linux Netkit ftp client was fixed years ago]
The Hackademy School, Journal & Audit
============ FULL DISCLOSURE GOING ILLEGAL IN FRANCE =======================
Legal notice (should be obvious), because of a new french law - yet to be
adopted - prohibiting among other things the disclosure of tools and data
aimed as committing cyber crimes :
"No warranty of any kind. Advisory published in an intent to help system
administrators to apply patches and workarounds to secure their networks
and systems. These data are not aimed to help anyone doing any illegal
actions. Such unfair uses of these informations are forbidden."
*** Please fight against this irresponsible law. In a few weeks, if you are
french and a virus infects your computer, you will be outlaw. If you are
curious and download nmap/nessus, but don't have any personal network to
scan, you will be outlaw. But if you are a virus writer, this is "for
research", so you will have no problem with this law. Wow, how good.***