Software Engineering Institute

Yahoo! Webcam is a component of Yahoo! Messenger that allows users to chat via webcams over a network. Yahoo! Webcam Viewer includes an ActiveX control provided by the file ywcvwr.dll . This ActiveX control contains a stack buffer overflow vulnerability in the Server property.

We are aware of publicly available exploit code for this vulnerability.

By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message or attachment), an attacker may be able to execute arbitrary code with the privileges of the user. The attacker could also cause Internet Explorer (or the program using the WebBrowser control) to crash.

Apply an update
This issue is addressed in Yahoo! Messenger 8.1. If you are unable to upgrade, please consider the following workarounds:

Disable the Yahoo! Messenger ActiveX control in Internet Explorer

The vulnerable ActiveX control can be disabled in Internet Explorer by setting the kill bit for the following CLSID:

(9D39223E-AE8E-11D4-8FD3-00D0B7730277)

More information about how to set the kill bit is available in Microsoft Support Document 240797. Alternatively, the following text can be saved as a .REG file and imported to set the kill bit for this control:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{9D39223E-AE8E-11D4-8FD3-00D0B7730277}]
"Compatibility Flags"=dword:00000400

Disable ActiveX

Disabling ActiveX controls in the Internet Zone (or any zone used by an attacker) appears to prevent exploitation of this and other ActiveX vulnerabilities. Instructions for disabling ActiveX in the Internet Zone can be found in the "Securing Your Web Browser" document.