[NT] Format String and Buffer Overflow in the IRC Client of Trillian

From: support@securiteam.com
Date: 08/05/02


From: support@securiteam.com
To: list@securiteam.com
Date: Mon,  5 Aug 2002 19:10:31 +0200 (CEST)

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  Format String and Buffer Overflow in the IRC Client of Trillian
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SUMMARY

 <http://www.trillian.cc/> Trillian is an all in one instant messaging
tool. The tool however has been found to contain two security
vulnerabilities that would allow a remote attacker to cause the client to
execute arbitrary code.

DETAILS

INVITE Format String Vulnerability:
There exists a format string vulnerability in the way Trillian handles
channel invites. The vulnerability is invoked by merely joining a channel
with a name of the sorts of: #%n%n%n, and inviting your victim into it.
Further, by using a specially crafted invite message, it is possible to
overwrite the EIP or the EBP.

While the format strings exploit would be a hard to write, treating this
as a text book buffer overflow by using a string like #%4095x<some 4 byte
address here>, you can overwrite EIP with ease. The only problem with
exploitation after overwriting EIP is getting the large win32 shellcode
into some area in the memory where it can be located, and where it will be
not broken up.
This is because IRC messages allow only 448 bytes per message. As an
alternative it might be possible, though, to initiate a DCC chat with the
user (which they would have to accept) and store the shellcode there.
Another option is to store the shellcode in multiple messages and have the
shellcode itself jump around, either way exploitation is not trivial.

DCC Chat Buffer Overflow:
The second vulnerability, the buffer overflow is entirely unrelated to the
above, but exists in the DCC chat itself. Flooding the user with about
4282 characters in one DCC message will overwrite EAX.

ADDITIONAL INFORMATION

The information has been provided by <mailto:josh@pulltheplug.com> Josh,
and <mailto:mtwoar@hotmail.com> omega.

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