Public Vulnerability Reports

Microsoft Internet Explorer 9 CFormElement Use-after-Free Vulnerability

11.13.12

BACKGROUND

Internet Explorer is Microsoft's web browser for the Windows platform.

DESCRIPTION

Remote exploitation of a use-after-free vulnerability in Microsoft Corp.'s Internet Explorer 9 could allow an attacker to execute arbitrary code with the privileges of the current user. The vulnerability occurs when the innerHTML property of an element containing a button element is modified. This triggers a DOM event that frees the button object; however, a stale reference to the button object remains and is later reused. This can lead to memory corruption and 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 that an attacker created. 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.

To exploit this vulnerability, it is necessary to control heap data in the chunk that is freed and reused. Testing has demonstrated that this can be performed reliably.

DETECTION

This vulnerability exists in Internet Explorer 9.

WORKAROUND

Several workarounds involving disabling or restricting site access to ActiveScript can be employed to make exploitation more difficult; however, this will not prevent the vulnerability from being exploited if the user refreshes the page manually. The following workarounds can be employed to disable scripting:

  • Set Internet and Local intranet security zone settings to "High" to block ActiveX Controls
  • and Active Scripting in these zones. Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone; add trusted sites to the Internet Explorer trusted sites zone.
Keep in mind that disabling or restricting scripting can severely impact the usability of the browser.

VENDOR RESPONSE

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

http://technet.microsoft.com/en-us/security/bulletin/ms12-071

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2012-1538 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

08/08/2012 Initial Vendor Notification
08/08/2012 Initial Vendor Reply
11/13/2012 Coordinated Public Disclosure

CREDIT

This vulnerability was reported to iDefense by Jose A. Vazquez of spa-s3c.blogspot.com

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

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

LEGAL NOTICES

Copyright © 2012 Verisign, 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 customer service 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.