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iDEFENSE Security Advisory 04.12.05: Microsoft Internet Explorer DHTML Engine Race Condition Vulnerability

From: iDEFENSE Labs (labs-no-replyidefense.com)
Date: Tue Apr 12 2005 - 13:43:39 CDT

Microsoft Internet Explorer DHTML Engine Race Condition Vulnerability

iDEFENSE Security Advisory 04.12.05
April 12, 2005


Internet Explorer is a set of core technologies in Microsoft Windows
operating systems that provide web browsing functionality. Further
information is available at:


Dynamic HTML (DHTML) is built on an object model that extends the
traditional static HTML document to enable web authors to create more
engaging and interactive Web pages. DHTML provides authors with enhanced

creative control so they can manipulate any page element at any time.
More information is available at:



Remote exploitation of a race condition vulnerability in version 6 of
Microsoft Corporation's Internet Explorer web browser could allow the
execution of arbitrary code under the privileges of the currently logged

in user.

Internet Explorer supports dynamic creation of HTML elements with
JavaScript using various DHTML methods such as createElement(),
appendChild(), and removeNode(). A number of problems have been found in

the implementation of these objects and methods, including some which
can be exploited to cause execution of arbitrary code.

The problem specifically exists within the memory management routines of

Internet Explorer's object handling code. In some situations one thread
reads data from memory that has either been overwritten by another
thread or has not yet been initialized by another thread. This can lead
to random crashes and remote command execution.


Successful exploitation allows remote attackers to execute arbitrary
code in the context of the user running the Internet Explorer process.
Exploitation will not be 100% reliable. However, proof of concept
exploit code was generated with reliable execution approximately 90% of
the time.

In order to exploit this vulnerability an attacker must convince the
victim to visit a web site, or cause malicious DHTML code to be rendered
by Internet Explorer using some other technique, such as a persist ant
XSS (cross-site scripting) attack on a trusted site.


iDEFENSE has confirmed the existence of this vulnerability in the
following Microsoft Internet Explorer versions:

    6.0.2900.2180 on Windows XP Professional with Service Pack 2.
    6.0.2800.1106 on Windows XP Professional with Service Pack 1.
    6.0.2800.1106 on Windows 2000 Professional with Service Pack 4.

It is suspected that all versions of Internet Explorer 6.0 are affected.


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
2. Click the Security tab and the Custom Level button.
3. Under Scripting, then Active Scripting, click the Disable radio


This vulnerability is addressed in Microsoft Security Bulletin MS05-020
available at:



The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0553 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.


10/25/2004 Initial vendor notification
10/25/2004 Initial vendor response
04/12/2005 Coordinated public disclosure


Berend-Jan Wever (skylined[at]edup.tudelft.nl,
http://www.edup.tudelft.nl/~bjwever/) is credited with this discovery.

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Copyright (c) 2005 iDEFENSE, Inc.

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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.