Software Engineering Institute

Cisco WebEx is an online meeting and collaboration software package. WebEx Meeting Manager is the client-side application that is used by the WebEx meeting service. WebEx Meeting Manager includes an ActiveX control called WebexUCFObject, which is provided by the file atucfobj.dll. The WebexUCFObject ActiveX control contains a stack buffer overflow in the NewObject() method.

Limited testing has indicated that not every version of the WebexUCFObject ActiveX control is marked as Safe For Scripting, which means that some versions of the control may not be exploitable by using a default configuration of Internet Explorer. The Cisco Security Advisory indicates that WBS 23, WBS25, and WBS26 are vulnerable.

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.

Apply an update
The Cisco Security Advisory indicates that WebEx meeting participants will automatically receive a fixed version of atucfobj.dll when they join a meeting on a server with fixed software. Version 26.49.9.2838 is the first fixed version for WBS 26 users.

Disable the WebexUCFObject ActiveX control in Internet Explorer

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

{E06E2E99-0AA1-11D4-ABA6-0060082AA75C}
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\{E06E2E99-0AA1-11D4-ABA6-0060082AA75C}]
"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.