iDefense Security Advisory 12.14.10 http://labs.idefense.com/intelligence/vulnerabilities/ Dec 14, 2010 I. BACKGROUND Internet Explorer is a graphical web browser developed by Microsoft Corp. that has been included with Microsoft Windows since 1995. For more information about Internet Explorer, please the visit following website: http://www.microsoft.com/ie/ II. DESCRIPTION Remote exploitation of a memory corruption vulnerability in Microsoft Corp.'s Internet Explorer could allow an attacker to execute arbitrary code with the privileges of the current user. The vulnerability exists due to an uninitialized variable in the "CLayout::EnsureDispNode" method. This method is called to recalculate the location of various HTML elements within the page. This function passes a "CDispNodeInfo" object to another function, "CLayout::GetDispNodeInfo," which is supposed to initialize the object passed in; however, the function fails to properly initialize a flag's value that is used later to determine how many "extra" bytes to allocate for a heap buffer. This eventually leads to an undersized buffer being allocated to hold a "CDispClipNode" object in the "CLayout::EnsureDispNodeCore" function. The vulnerability manifests itself when the "CDispNode::SetUserClip" function attempts to use the invalid "extra size" to calculate an offset into the object and manipulate a bit at this location. This corrupts the objects VTABLE by setting the second bit to 1, which can lead to the execution of arbitrary code when this pointer is accessed later. 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. 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 Microsoft Internet Explorer 6, 7 and 8 are vulnerable. V. WORKAROUND Microsoft suggested workarounds can be found in Microsoft Security Bulletin MS10-090. VI. VENDOR RESPONSE Microsoft Corp. has released patches which address this issue. Information about downloadable vendor updates can be found by clicking on the URLs shown. http://www.microsoft.com/technet/security/Bulletin/MS10-090.mspx VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2010-3962 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 08/11/2010 Initial Vendor Notification 08/11/2010 Initial Vendor Reply 12/14/2010 Coordinated Public Disclosure IX. CREDIT This vulnerability was reported to iDefense by José Antonio Vázquez González. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2010 iDefense, 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 customerservice@idefense.com 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.