Software Engineering Institute

IncrediMail is an email application that includes animations and 1000's of emoticons. IncrediMail comes with an ActiveX control called IMMenuShellExt, which is provided by the file ImShExt.dll. This ActiveX control contains a stack buffer overflow vulnerability in the DoWebMenuAction() method.

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.

We are currently unaware of a practical solution to this problem. Please consider the following workarounds

Disable the IMMenuShellExt ActiveX control in Internet Explorer

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

{F8984111-38B6-11D5-8725-0050DA2761C4}
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\{F8984111-38B6-11D5-8725-0050DA2761C4}]
"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.