Secunia

Two vulnerabilities have been identified in Yahoo! Chat and Messenger possibly allowing malicious people to execute arbitrary code through HTML documents.

The problem is that the "TargetName" parameter isn't properly verified in Yahoo! Webcam Viewer Wrapper ActiveX control. This can be exploited to cause both a stack and a heap based overflow which possibly could lead to execution of arbitrary code.

Another problem has been identified in the handling of the "AppId" parameter in the YInstStarter ActiveX control. This may be exploited to cause a heap overflow which could lead to execution of arbitrary code.

Solution
Remove all Yahoo! ActiveX controls and reinstall the software from Yahoo!.
Further details available in Customer Area

Provided and/or discovered by
Cesar Cerrudo

Original Advisory
http://messenger.yahoo.com/messenger/security/
(Page trying to detect if you need the update)

Deep Links
Links available in Customer Area