Description : Protocol Handler allow arbitrary switch to be passed to the associated program.<BR>
Exploit :
The protocol handler are defined in HKEY_CLASSES_ROOT. We will use the MMS protocol for this exemple. In the HKEY_CLASSES_ROOT\MMS\SHELL\OPEN\COMMAND Registry key you can see that the program associated with the MMS protocol is called through "C:\Program Files\Windows Media Player\wmplayer.exe" "%L". (In this cases, this is windows media player).
Now if we pass in to IE this string mms:\\."%20/layout%20c , the "%L" in the handler will now be "." /layout c". The /layout switch will open windows media player in Skin Mode.
<A HREF=mms:\\."%20/layout%20c>TRY IT</A>
Of course, the vulnerability is not to open WMP in Skin Mode but it reside in the hability to pass extra command line switches where only one should be accepted.
Nicolas Robillard, GSEC Information Security Advisor, Systems Security Group
