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From: trihuynh at (Tri Huynh)
Subject: Yahoo Instant Messenger Long Filename Downloading Buffer Overflow

Yahoo Instant Messenger Long Filename Downloading Buffer Overflow

 PROGRAM: Yahoo Instant Messenger (YIM)


 YIM is one of the most popular instant messengers. This is a cool product
that supports many  useful features like audio/video chatting, file

Fore more details about the product, please go to


By sending a specially crafted long filename to a user, an attacker can
cause a buffer overflow when the user's YIM tries to download the file
from the server. (No need to run the file).

For a fast demonstration, you can create a file like this
 "test<insert around 210 spaces here>.jpg" and send it to
another user and ask her to download it.

Because this is a buffer overflow, there is always a possibility to
run malicious code on the user's machine.

NOTE : This vulnerability is different from the one was discovered by
Hat-Squad team in October.


Yahoo has been contacted at and I got no response
except that they said the are looking to it...and here is the interesting
story on how
Yahoo handle it (after my little investigation) which I quote from an email
I sent
 to a friend in the PenetrationGroup about the issue (sorry for my laziness
8-)  :

"I already contacted Yahoo couple days ago...
.......After reading your email, I removed my YIM and downloaded the new one
from their
website and you are right; the newest version is not vulnerable.
there is NO WAY to upgrade from 5.6.0.xxxx to except you
YIM; and of course Yahoo doesn't tell anybody about it either.

If you go to you will see
there is
no update for this vulnerability. Again, the only way to patch it is
reinstall YIM
which Yahoo doesn't say anything about it.
(FYI, This vulnerability lays in the file ft.dll which is used to hande file
transferring in YIM.
They do patch this file in the new version, however if you want to dig more
into this thing, you can always get the old file from any of the YIM users
you know easily since nobody reinstall their YIM for no reason.)

So here is the new Yahoo! security strategy. Instead of informing the users
issueing a patch, they slip the patch into their main program silently and
say nothing about the vulnerability.  Doing so, they can avoid
 the press to embarass them for leaving so many vulnerabilities in their
product. However,
it is also a big embarassment if they protect ONLY new users who download
the new version and leave millions of other users who are using the old
version with
no patches available and are uninformed of the vulnerability. Yahoo !.....

The only way to patch it is removing and reinstalling YIM from Yahoo
website. Don't
waste your time to look for a patch in the messenger security page or any
info about this vulnerability
from them.  They don't give a damn !


 Discovered by Tri Huynh from SentryUnion


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