Software Engineering Institute

ActiveX

ActiveX is a technology that allows programmers to create reusable software components that can be incorporated into applications to extend their functionality. Internet Explorer is a common Windows application that makes use of ActiveX controls.

HTML Help Control

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 problem

The HHCtrl Object contains a heap overflow vulnerability when the Image property of the control is set. When the Image property is set multiple times, the heap memory can be corrupted.

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 vulnerability is addressed in Microsoft Security Bulletin MS06-046.

Disable ActiveX

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