Skype callto:// BoF technical details
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