Software Engineering Institute

The HTML Help Control (HHCtrl Object) is a Windows ActiveX control that provides the ability to view HTML help files. The HHCtrl Object is included in the file hhctrl.ocx and provides the ProgID (Programmatic Identifier) of Internet.HHCtrl. The HHCtrl Object fails to properly validate input.

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

This issue is addressed in Microsoft Security Bulletin MS07-008. This update provides a newer version of the HHCtrl Object.

Disable the HTML Help ActiveX control in Internet Explorer

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

{52a2aaae-085d-4187-97ea-8c30db990436}
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\{52a2aaae-085d-4187-97ea-8c30db990436}]
"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.