iDefense Security Advisory 07.20.11: Safari WebKit TIFF Use-After-Free Vulnerability

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

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 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. <BR>
<BR> 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.

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

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.

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-2011-0215 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/&#41;, which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

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

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X. LEGAL NOTICES

Copyright A© 2011 Verisign

Permission is granted for the redistribution of this alert
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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.