[ISN] EEYE: Yahoo! Mail Account Filter Overflow Hijack

[Drew Copley]

"Yahoo! Mail" Account Filter Overflow Hijack

Release Date:
April 19, 2004

Date Reported:
March 10, 2004

Severity:
High

Vendor:
Yahoo!

Description:
"Yahoo! Mail" is one of the Internet's most popular 
web based email solutions. They provide free email and 
large capacity storage, as well as subscription-based 
services such as mail forwarding, expanded storage and 
personalized email addresses. 

eEye Digital Security has discovered a security hole in 
"Yahoo! Mail" which allows a remote attacker to take over 
an account remotely by sending a specially crafted email.

Technical Description:
-----------EXAMPLE EMAIL---------

SCRIPT
[->a bunch of chars here [spaces are most stealth], the whole 
file size will be just about 100KB]
[this causes the filter to not work... the code is then run 
automatically]


---------------------------------

The pseudo-diagram above explains the scenario rather well. 
For whatever reason, Yahoo's email filter simply does not 
work on files which exceed a certain range. This kind of 
software issue is relatively common. 

A remarkable note about this bug is that no one seems to 
have found it before. 

As far as anyone knows.



Drew's Happy-Happy Quote for the Day:

Ben Franklin, "Three can keep a secret if two are dead."

Protection:
Yahoo! Mail is a hosted, web based service, hence users 
do not need to patch. Yahoo has already fixed this bug, 
therefore all Yahoo accounts are now completely safe from
it.

Vendor Status:
Yahoo! has been notified and has rectified the issue.

Credit:
Drew Copley, eEye Digital Security (dcopley eeye.com), Research Engineer
thanks to "http-equiv" for additional research

Related Links:
Retina Network Security Scanner - Free 15 Day Trial 
http://www.eeye.com/html/Products/Retina/download.html

Greetings:
To all of you out there that don't use turn signals. 
Sooner or later your time is going to come. And a special 
greeting to all of these competitors of ours making some extra 
cash by selling pre-fix vulnerabilities through pay for play 
"mailing lists". I am sure North Korea, the Yakuza, the 
"Triads", the Russian Mafiya, La Costa Nostra, and every 
other criminal state or organization appreciates your type of 
"Partial Full Disclosure for a Darn Good Price" motto.

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