Software Engineering Institute

The registration process for British Telecommunications (BT) internet services uses an ActiveX control called webhelper. This ActiveX control is provided by the file btwebcontrol.dll. The BT Consumer webhelper ActiveX control contains multiple buffer overflow vulnerabilities.

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.

This issue is addressed in version 2.0.0.8 of the Consumer webhelper ActiveX control. However, customers who have already gone through the registration process will not likely get the updated control. Therefore, please consider the following workarounds

Disable the BT Consumer webhelper ActiveX control in Internet Explorer

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

{EC5A4E7B-02EB-451D-B310-D5F2E0A4D8C3}

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\{EC5A4E7B-02EB-451D-B310-D5F2E0A4D8C3}]
"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.