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Security Services

Microsoft Internet Explorer onmove Use-after-Free Vulnerability



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


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.


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.


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


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.


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


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 (, which standardizes names for security problems.


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


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2012 Verisign, Inc.

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