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Safari WebKit TIFF Use-After-Free Vulnerability

07.20.11

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/

DESCRIPTION

Remote exploitation of a use-after-free vulnerability in WebKit, as included with Apple Inc.'s Safari Web browser, could allow an attacker to execute arbitrary code with the privileges of the current user.

The vulnerability occurs during the processing of a malformed TIFF image. Specifically, it is possible to trigger a use-after-free vulnerability when Safari fails to properly release an object. The object's memory is freed; however, a reference to the object remains. When the reference is later used to access the object, this now invalid memory is treated as a valid object and the object's vtable is used to make an indirect function call. This may result in the execution of arbitrary code.

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.

DETECTION

Safari versions prior to 5.1 and 5.0.6 are vulnerable.

WORKAROUND

iDefense is currently unaware of effective workarounds for this vulnerability, as it is not possible to disable TIFF support; however, disabling JavaScript will make it more difficult to exploit the vulnerability.

VENDOR RESPONSE

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

http://support.apple.com/kb/HT4808

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2011-0215 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

02/02/2011 Initial Vendor Notification
02/02/2011 Initial Vendor Reply
07/20/2011 Coordinated Public Disclosure

CREDIT

This vulnerability was reported to iDefense by Juan Pablo Lopez Yacubian.

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LEGAL NOTICES

Copyright © 2011 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.