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Microsoft Internet Explorer onmove Use-after-Free Vulnerability

21.09.12

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 (IE) could allow an attacker to execute arbitrary code with the privileges of the current user. The specific flaw exists within the way IE executes the "onmove" event handler. When an "onmove" event triggers, the "onmove" event handler dynamically modifies a page's content and frees an object while a reference to it remains. This reference is later reused, potentially leading to a stale object being accessed. The result of this could allow an attacker to execute 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 has created. An attacker typically accomplishes this via social engineering or injecting content into compromised, trusted sites. After a user visits such a malicious Web page, no further user interaction is needed.

To exploit this vulnerability, an attacker needs to have some control of the heap to reallocate the freed pointer. The browser provides an ideal environment for this control, so exploitation is relatively straightforward.

DETECTION

iDefense has confirmed the existence of this vulnerability in IE 8 and 9, while IE 6 and 7 are not affected by this vulnerability.

WORKAROUND

Several workarounds involving disabling or restricting site access to ActiveScript can be employed to mitigate this vulnerability. This includes the following:

  • Set Internet and local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones
  • Configure IE to prompt before running Active Scripting or to disable Active Scripting in the Internet and local intranet security zones; add trusted sites to the IE trusted sites zone.

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/ms12-063

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2012-1529 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

06/13/2012 Initial Vendor Notification
06/13/2012 Initial Vendor Reply
09/21/2012 Coordinated Public Disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2012 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.