Software Engineering Institute

Microsoft COM

Microsoft COM is a technology that allows programmers to create reusable software components that can be incorporated into applications to extend their functionality. Microsoft COM includes COM+, Distributed COM (DCOM), and ActiveX Controls.

ActiveX controls

ActiveX controls are COM objects that have visual elements. ActiveX controls are traditionally designed to be used in Internet Explorer. A web page can make use of an ActiveX control in various ways, such as by referencing its Class Identifier (CLSID) in an HTML OBJECT tag.

The Problem

Internet Explorer will attempt to instantiate any COM object that is referenced by a web page. Certain COM objects that are not designed for use in Internet Explorer may cause unexpected results, such as executing arbitrary code or crashing the browser.

Exploit code for these vulnerabilities are publicly available.

By convincing a user to view a specially crafted HTML document (e.g., a web page, an HTML email message, or an email attachment), an attacker could execute arbitrary code with the privileges of the user. The attacker could also cause IE (or the program using the WebBrowser control) to crash.

Apply An Update
Apply the appropriate update, as specified in Microsoft Security Bulletin MS06-042. This update sets the "kill bit" for certain CLSID values of COM objects known to be vulnerable. The MS06-042 update is similar to MS06-021, MS06-013, MS05-054, MS05-037, MS05-038, and MS05-052, but it includes additional COM objects.

Microsoft has listed several workarounds in the Microsoft Security Bulletin, including disabling ActiveX controls.