Public Vulnerability Reports

Multiple Vendor Microsoft ATL/MFC ActiveX Security Bypass Vulnerability



Microsoft's Component Object Model (COM) was designed to allow interoperability between disjointed software components. It is a standardized interface solution to the programming dilemmas involved in object oriented programming, distributed transactions, and inter-language communications. COM is involved at some level in DDE, OLE, COM+, ActiveX, and DCOM. COM objects can be embedded in various document formats, Web Pages, and various other media technologies. Microsoft's Active Template Library (ATL) is a set of C++ templates that simplify developing COM objects. More information on COM and ATL can be found at the following URLs.


Remote exploitation of a logic flaw vulnerability in Microsoft Corp.'s ATL/MFC ActiveX code, as included in various vendors' ActiveX controls, could allow attackers to bypass ActiveX security mechanisms.

One aspect of COM is a process called initialization. This process allows a program to load and store a COM object within various containers, such as OLE compound storage files and raw streams.

Depending upon certain characteristics of an OLE component designed with the Microsoft ATL, it is possible to cause one component to initialize an arbitrary secondary component. Ordinarily this behavior would not be a cause for alarm, however, certain applications employ various methods to verify that a control is Safe for Initialization. One such application is Internet Explorer. More information on these methods can be found at

Standard operating procedure is to have the loading application perform the various security checks. However, a control marked "Safe for Initialization" that contains this vulnerability will not perform the same checks. By loading a vulnerable ActiveX control and passing in specially crafted persistent storage data, an attacker can bypass all of the typical security checks and load any ActiveX control without a warning.


Exploitation of this vulnerability allows an attacker to bypass security checks (such as kill-bits in Internet Explorer). Successful exploitation would require the attacker to convince his or her victim into visiting a specially crafted Web page leveraging the vulnerability. While there is no way to forcibly make a victim visit a website, exploitation may occur through normal Web browsing.

This vulnerability greatly increases the attack surface accessible via Internet Explorer by decreasing the amount of user interaction necessary to access other initialization vulnerabilities.


iDefense has confirmed the existence of this vulnerability inside Microsoft's ATL and MFC. Although later versions of the ATL/MFC are less vulnerable, certain conditions can trigger the same exploit pattern.

Any code compiled with these libraries may also be vulnerable. Specific controls compiled with vulnerable versions include Adobe Flash and Sun's Java plug-in.


iDefense is currently unaware of any workarounds for this issue.


Microsoft has released two security bulletins which address this issue. For more information, consult their advisories at the following URL:


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2009-2493 to this issue. This is a candidate for inclusion in the CVE list (, which standardizes names for security problems.


12/05/2008 Initial Contact
01/05/2009 Microsoft requested PoC
01/06/2009 iDefense sent PoC
01/23/2009 iDefense requested status update
01/26/2009 iDefense requested status update
01/27/2009 Microsoft reports status
02/09/2009 Microsoft reports status
02/26/2009 Microsoft reports status
03/27/2009 Microsoft reports status
04/23/2009 Microsoft reports status, predicts September release
05/13/2009 Microsoft reports status, predicts October release
05/21/2009 Microsoft requests conference call
06/03/2009 Conference call takes place
06/05/2009 Microsoft supplies corrected ATL headers and requests review
07/28/2009 Public disclosure via MS09-035 out-of-band bulletin
07/29/2009 Material presented at BlackHat USA
08/11/2009 Microsoft publishes MS09-037


This vulnerability was discovered by Ryan Smith of iDefense Labs.

Get paid for vulnerability research

Free tools, research and upcoming events


Copyright © 2009 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.