Both of the flaws, which allow for system hijacking, are boundary errors in two ActiveX controls in Yahoo Messengers Webcam Upload and Webcam Viewer.
Security researchers say that they expect attacks using the flaws to arrive soon. That makes prompt patching critical.
Yahoo has an update available, Version 126.96.36.1991, to fix the vulnerability, posted at messenger.yahoo.com. The company provided this statement on the issue:
"The Yahoo Messenger team recently learned of a buffer overflow security issue in an ActiveX control. Upon learning of this issue, we began working towards a resolution and implemented a fix to Yahoo Messengers software download. We are encouraging all Yahoo Messenger users to download the latest version (188.8.131.521) available at messenger.yahoo.com."
Yahoo also plans to introduce a new version of its IM client over the "next several weeks" which users will be prompted to download upon signing into the service.
The innocuous proof of concept code merely run Windows calculator, but the code poster—whose handle is "Danny"—says its "trivial" to change the shellcode. (Proof of concept code, or PoC, is often used as a synonym for a zero-day exploit that doesnt fully exploit a new vulnerability but provides code that shows how an exploit could be done). The exploit code is posted here on Neohapsis Archives.
"Great results! very relible, runs calc.exe, replace with shellcode of your choice!!!" Danny wrote.
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