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iDefense Security Advisory 03.11.10: Multiple Vendor WebKit HTML Element Use After Free Vulnerability
From: iDefense Labs <labs-no-reply () idefense com>
Date: Thu, 11 Mar 2010 19:01:42 -0500

iDefense Security Advisory 03.11.10
http://labs.idefense.com/intelligence/vulnerabilities/
Mar 11, 2010

I. BACKGROUND

WebKit is an open source web browser engine. It is currently used by
Apple Inc.'s Safari browser, as well as by Google's Chrome browser. For
more information, see the vendor's site at the following link.

http://webkit.org/

II. DESCRIPTION

Remote exploitation of a memory corruption vulnerability in WebKit, as
included with multiple vendors' browsers, could allow an attacker to
execute arbitrary code with the privileges of the current user.

The vulnerability occurs when a certain property of an HTML element is
reset via JavaScript code. When this occurs, a C++ object is
incorrectly accessed after it has been freed. This results in an
attacker controlled value being used as a C++ VTABLE, which leads to
the execution of arbitrary code.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the user viewing the Webpage. To exploit
this vulnerability, a targeted user must load a malicious Webpage
created by an attacker. An attacker typically accomplishes this via
social engineering or injecting content into compromised, trusted
sites. After the user visits the malicious Webpage, no further user
interaction is needed.

Exploitation of this vulnerability is relatively simple if a heap spray
technique is used to control large portions of heap memory. It is also
trivial for an attacker to reallocate the chunk of freed memory and
populate it with controlled values. This allows an attacker to control
a C++ VTABLE, which leads to code execution. As such, iDefense
considers this vulnerability to be highly exploitable.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Google
Chrome 3.0.195.38 and Safari 4.0.4. Previous versions are suspected to
be vulnerable. A full list of affected Apple products can be found in
Security Advisory APPLE-SA-2010-03-11-1 Safari 4.0.5.

V. WORKAROUND

The vulnerability is present in the JavaScript engine, so disabling
JavaScript is an effective workaround. This can be performed via the
command line with Google Chrome, and the Preferences menu in Safari.

VI. VENDOR RESPONSE

Apple Inc. has released a patch which addresses this issue. Information
about downloadable vendor updates can be found by clicking on the URLs
shown. http://www.apple.com/safari/download

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2010-0040 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

12/15/2009  Initial Vendor Notification
12/15/2009  Initial Vendor Reply
03/11/2010  Coordinated Public Disclosure

IX. CREDIT

This vulnerability was reported to iDefense by wushi&Z of team509.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php

Free tools, research and upcoming events
http://labs.idefense.com/

X. LEGAL NOTICES

Copyright © 2010 iDefense, 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 customerservice () idefense com 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.

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