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Microsoft XML Core Services XMLDOM Memory Corruption Vulnerability

08.14.07

BACKGROUND

XML Core Services (also known as MSXML) is a library for processing XML files. It works with, and was original part of, Internet Explorer. For more information visit the following URL.

http://msdn2.microsoft.com/en-us/xml/default.aspx
http://en.wikipedia.org/wiki/MSXML

DESCRIPTION

Remote exploitation of a buffer overflow vulnerability within Microsoft Corp.'s XML Core Services may allow an attacker to execute arbitrary code in the context of the current user.

The vulnerability specifically exists in incorrect checking being performed on the length argument to the substringData() method of an XMLDOM object. When certain length values are supplied, a large region of memory is copied into a buffer of insufficient size.

ANALYSIS

Exploitation of this vulnerability requires an attacker to convince a user to open a page containing a malicious script.

In testing by iDefense Labs, code execution was determined to be possible. Calling the vulnerable code with no other setup would simply cause the application to write (or sometimes read) past the end of the allocated memory and trigger an access violation exception. However, an attacker can cause pointers in use by another thread to be overwritten and may be able to execute code.

DETECTION

iDefense confirmed the existence of this vulnerability using Internet Explorer 6.x on Windows XP SP2. It is suspected that other versions are also affected.

WORKAROUND

Disable active scripting, if it is not necessary for daily operations, using the following steps.

 1. In IE, click on Tools and select Internet Options from the drop-down menu. 2. Click the Security tab and the Custom Level button. 3. Under Scripting, then Active Scripting, click the Disable radio button. 

VENDOR RESPONSE

Microsoft has addressed this vulnerability within Microsoft Security Bulletins MS07-042 and MS07-043. For more information, consult their bulletins at the following URLs.

http://www.microsoft.com/technet/security/Bulletin/MS07-042.mspx
http://www.microsoft.com/technet/security/Bulletin/MS07-043.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-2223 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

DISCLOSURE TIMELINE

05/17/2006 Initial vendor notification
05/17/2006 Initial vendor response
08/14/2007 Coordinated public disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 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.