Public Vulnerability Reports

Microsoft HxTocCtrl ActiveX Control Invalid Param Heap Corruption Vulnerability



The HxTocCtrl ActiveX Control is a library used by the Microsoft Help engine. More information is available at the following website.


Remote exploitation of a heap corruption vulnerability in Microsoft Corp.'s Microsoft Help 2.5 ActiveX control allows an attacker to execute arbitrary code with the privileges of the logged-on user.

Microsoft Help 2.5 installs the following ActiveX control, which is marked as safe for scripting:

ProgID: HxVz.HxTocCtrl.1
CLSID: 314111B8-A502-11D2-BBCA-00C04F8EC294
File: %PROGRAM DIR%Common FilesMicrosoft SharedHelphxvz.dll

By providing malformed arguments to this control, it is possible to corrupt heap memory.


Exploitation allows attackers to execute arbitrary code with the privileges of the logged-on user. Exploitation would require an attacker to host a maliciously crafted page on a website and entice users to visit that site. No further action is needed other than following a link to a malicious website. Exploitation requires that users have the specified control installed.


iDefense has confirmed this vulnerability in version 2.05.50727.42 of hxvz.dll, which is installed with Visual Studio 2005.

The following products might also include vulnerable versions of the control:

Visual Studio 2005
Visual Studio .NET 2003
Visual Studio .NET 2002
MSDN Library 2002 - Current
BizTalk Server 2004 Standard Edition


Setting the kill bit for this control mitigates the threat from web-based attacks that might be conducted via Internet Explorer. The vulnerable CLSID is:



Microsoft has officially addressed this vulnerability with Security Bulletin MS08-023. For more information, consult their bulletin at the following URL.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-1086 to this issue. This is a candidate for inclusion in the CVE list (, which standardizes names for security problems.


12/12/2006 Initial vendor notification
12/12/2006 Initial vendor response
04/08/2008 Coordinated public disclosure


The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research

Free tools, research and upcoming events


Copyright © 2008 Verisign, Inc.

Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customer service for permission.

Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.