iDefense Security Advisory 07.20.11: Apple Safari innerText Use-After-Free Vulnerability

iDefense Security Advisory 07.20.11
http://labs.idefense.com/intelligence/vulnerabilities/
Jul 20, 2011

I. BACKGROUND

Safari is Apple's web browser, and is based on the open source WebKit
browser engine. MobileSafari is Safari for Apple's mobile devices
including the iPad and iPhone. For more information, see the vendor's
site found at the following link.

http://www.apple.com/safari/

II. DESCRIPTION

Remote exploitation of a memory corruption vulnerability in Apple Inc.'s
Safari browser could allow an attacker to execute arbitrary code with
the privileges of the current user.

Safari is Apple's Web browser and is based on the open source WebKit
browser engine.

This vulnerability occurs when Safari incorrectly handles an error state
when encountering a broken XHTML tag. Specifically, the tag enclosing
the tag being processed is freed and is then referenced after it has
already been freed. This can lead 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 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.

IV. DETECTION

Safari versions prior to 5.1 and 5.0.6 are vulnerable.

V. WORKAROUND

Disabling JavaScript is an effective workaround for this vulnerability.

VI. 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

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2011-0234 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

06/01/2011 Initial Vendor Notification
06/01/2011 Initial Vendor Reply
07/20/2011 Coordinated Public Disclosure

IX. CREDIT

This vulnerability was reported to iDefense by wushi of team509.

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X. LEGAL NOTICES

Copyright A© 2011 Verisign

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
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part of this alert in any other medium other than electronically, please
e-mail [email protected] 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.