Vulnerability Note VU#732479

Internet Explorer CMarkup use-after-free vulnerability

Original Release date: 14 Feb 2014 | Last revised: 19 Feb 2014


Microsoft Internet Explorer contains a use-after-free vulnerability in the MSHTML CMarkup component, which can allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system.


Microsoft Internet Explorer contains a use-after-free vulnerability in the CMarkup component of the MSHTML library. This can allow for arbitrary code execution. We have confirmed Internet Explorer 10 to be vulnerable. It has been reported that Internet Explorer 9 is also affected. Other versions of Internet Explorer may also be affected.

Note that this vulnerability is being exploited in the wild, and the exploit code is publicly available. The exploit in the wild currently only targets Internet Explorer 10 on systems that have Adobe Flash installed and do not have EMET installed. Windows 8 comes with Flash, so no additional software is required to be vulnerable to this particular exploit on that platform. Although no Flash vulnerability appears to be at play here, the Internet Explorer vulnerability is used to corrupt Flash content in a way that allows ASLR to be bypassed via a memory address leak. This is made possible with Internet Explorer because Flash runs within the same process space as the browser. The Flash content uses this ASLR bypass to disable DEP and then execute code. The Microsoft.XMLDOM ActiveX control is used to determine if EMET is installed on the target system. This is done by checking for the presence of C:\Windows\AppPatch\EMET.dll. If this file is present, the exploit attempt is aborted.


By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message or attachment), an attacker may be able to execute arbitrary code.


Install the Microsoft Fix it
Microsoft Security Advisory (2934088) has been released to describe this issue. This advisory references a Fix it utility to address this vulnerability.

Please also consider the following workarounds:

Use the Microsoft Enhanced Mitigation Experience Toolkit

The Microsoft Enhanced Mitigation Experience Toolkit (EMET) can be used to help prevent exploitation of this vulnerability. CERT/CC has created a video tutorial for setting up EMET 3.0 on Windows 7. Note that platforms that do not support ASLR, such as Windows XP and Windows Server 2003, will not receive the same level of protection that modern Windows platforms will.

Update to Internet Explorer 11

The public exploit for this vulnerability does not work with Internet Explorer 11.

Vendor Information (Learn More)

VendorStatusDate NotifiedDate Updated
Microsoft CorporationAffected14 Feb 201419 Feb 2014
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base 10.0 AV:N/AC:L/Au:N/C:C/I:C/A:C
Temporal 9.5 E:H/RL:W/RC:C
Environmental 9.5 CDP:ND/TD:H/CR:ND/IR:ND/AR:ND



This vulnerability was publicly reported by FireEye.

This document was written by Will Dormann.

Other Information

  • CVE IDs: CVE-2014-0322
  • Date Public: 13 Feb 2014
  • Date First Published: 14 Feb 2014
  • Date Last Updated: 19 Feb 2014
  • Document Revision: 46


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