AOL Instant Messenger version 4.1.2010 (others?) appears to be vulnerable to

a DoS attack when handling file transfers with filenames containing %s.



The problem I encountered is that trying to send a file to crash my victim's

client would cause my client to crash first, defeating the purpose.  To get

around this, I got a copy of the Netscape/AOL Instant Messenger client

available on Netscape's site which doesn't seem to be vulnerable to this

bug.  I created a file called %s%s%s%s%s%s%s%s%s%s.jpg and sent it as a file

transfer to my victim, causing their client to crash immediately.  There is

an option in AIM to generate a warning before accepting messages or file

transfers from people that aren't in your buddy list.  Enabling this option

did generate the warning, but did not stop the client from crashing.



This is not my area of expertise, but this DoS is apparently related to a

problem with format strings. I am unable to determine whether or not it is

further exploitable beyond a simple DoS.





-SpunOne

http://www.FAZED.net







Another interesting note is that creating a file named:

%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s

%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s

%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s

%s%s%s%s.jpg seems to do funny things to explorer.exe in WinME (explorer

crashes) and Win98 when trying to view the properties of the file.