Software Engineering Institute

Yahoo Messenger is an instant messaging application. Yahoo Messenger includes several ActiveX controls. The YMailAttach ActiveX control, which is provided by ymmapi.dll, contains a buffer overflow 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

As specified in the Yahoo Security Update, this issue is addressed in versions of Yahoo Messenger from Nov 2nd 2006 or later. Version 2005.1.1.4 or higher of ymmapi.dll contains the fix.

Disable the YMailAttach ActiveX control in Internet Explorer

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

 {AA218328-0EA8-4D70-8972-E987A9190FF4}
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\{AA218328-0EA8-4D70-8972-E987A9190FF4}]
"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.