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Multiple Vendor WebKit Error Handling Use After Free Vulnerability

06.08.09

BACKGROUND

WebKit is an open source web browser engine. It is currently used by the 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/

DESCRIPTION

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

The vulnerability occurs when JavaScript code is used to set a certain property of an HTML tag within a web page. When JavaScript code sets this property, child elements of the tag are freed. However, when an error in the remaining HTML is encountered, these previously freed tag values are referenced. The freed memory is then treated as a C++ object, which can lead to attacker controlled values being used as function pointers.

ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the user viewing the web page. To exploit this vulnerability, a targeted user must load a malicious web page 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 web page, no further user interaction is needed.

WebKit is used by multiple applications, including Google Chrome and Apple Safari (including Safari on the iPhone). Affected versions are listed in the Detection field of this report.

DETECTION

iDefense has confirmed the existence of this vulnerability in WebKit-r42162. Previous versions may also be affected. Additionally, the following applications that use WebKit have been determined to be vulnerable:

 Google Chrome 1.0.154.53 Safari 3.2.1 (5525.27.1) Safari 3.1.1 running on iPhone 2.2.1 (5525.27.1) 

WORKAROUND

Disabling JavaScript will prevent exploitation of this vulnerability.

VENDOR RESPONSE

Apple Inc. has released a patch which addresses this issue. For more information, consult their advisory at the following URL:

http://support.apple.com/kb/HT3613

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2009-1690 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

04/13/2009 - Initial Contact
04/14/2009 - Initial response
04/22/2009 - PoC Requested
04/23/2009 - PoC Sent
05/18/2009 - Apple inquiry about Safari 4
05/21/2009 - Responded to Apple inquiry
06/08/2009 - Coordinated public disclosure

CREDIT

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

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LEGAL NOTICES

Copyright © 2009 Verisign, 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.