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Re: Skype callto:// BoF technical details



Berend-Jan Wever wrote:

Skype reported they've found a remotely exploitable BoF in the callto:// URI 
handler. New version has been released.
http://www.skype.com/products/skype/windows/changelog.html
http://secunia.com/advisories/13191/

Technical details:

The bufferoverflow happens when a skype user clicks on a "callto://username" 
link with a username longer then 4096 characters that does not exist: An error message is 
created and put into a buffer without correct size checks. The errormessage and buffer 
are unicode but unicode characters are filtered out and replaced with '?'. Only printable 
ascii characters seem to get through. A return address can be overwritten as well as the 
SEH. Exploitation is complicated by the fact that return addresses have to be in range 
0x00??00??.

Webbrowsers like MSIE do not support URI's long enough to trigger the BoF. To 
exploit it, one could send a skype user a callto:// link in a private message 
and trick him/her into clicking it.

If one would want to, one could write a skype worm with this. User interaction 
would be required: they'd have to click the link.

Cheers,
SkyLined



They fixed it without knowing of the callto:// thing I suppose cause I wrote them an email saying that the quick-call field is exploitable, too. This was fixed within the new version. Maybe your flaw is fixed, too, if not, I think it soon will be :)