Microsoft Internet Explorer VML stack buffer overflow

Overview

Microsoft Internet Explorer (IE) fails to properly handle Vector Markup Language tags. This vulnerability may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system.

Description

Microsoft IE version 5.0 and higher supports the Vector Markup Language (VML), which is a set of XML tags for drawing vector graphics. IE fails to properly handle malformed VML tags allowing a stack buffer overflow to occur. If a remote attacker can persuade a user to access a specially crafted web page with IE, that attacker may be able to trigger the buffer overflow. In addition, an attacker could deliver an HTML email message or entice a user to select an HTML document in Windows Explorer.

On Windows XP SP2 systems the vulnerable component (VGX.DLL) is compiled with the /GS (Buffer Security Check) flag. However, exploits using techniques to circumvent the Buffer Security Check are publicly available.

Note that this vulnerability is actively being exploited.

---

Impact

A remote, unauthenticated attacker can execute arbitrary code on a vulnerable system.

---

Solution

Apply the update from Microsoft

Microsoft addresses this vulnerability with the update listed in Microsoft Security Bulletin MS06-055.

---

Until the update can be applied, consider the following workarounds:

Disable VML support

Microsoft Security Advisory (925568) suggests the following techniques to disable VML support:

* Un-register Vgx.dll on Windows XP Service Pack 1; Windows XP Service Pack 2; Windows Server 2003 and Windows Server 2003 Service Pack 1[](<javascript:Toggle\('s11l3-ESH'\)>)[](<javascript:Toggle\('s11l3-ESH'\)>)
* Modify the Access Control List on Vgx.dll to be more restrictive
* Configure Internet Explorer 6 for Microsoft Windows XP Service Pack 2 to disable Binary and Script Behaviors in the Internet and Local Intranet security zone

Do not follow unsolicited links

In order to convince users to visit their sites, attackers often use URL encoding, IP address variations, long URLs, intentional misspellings, and other techniques to create misleading links. Do not click on unsolicited links received in email, instant messages, web forums, or internet relay chat (IRC) channels. Type URLs directly into the browser to avoid these misleading links. While these are generally good security practices, following these behaviors will not prevent exploitation of this vulnerability in all cases, particularly if a trusted site has been compromised or allows cross-site scripting.

Disable Active Scripting

Although this vulnerability does not require Active Scripting to be enabled, known exploits targeting this issue use Active Scripting to place malicious code on a vulnerable system. To block this attack vector, it is recommended that Active Scripting be disabled. For instructions on how to disable Active Scripting in Microsoft Internet Explorer, please refer to the Internet Explorer section of the Securing Your Web Browser document.

Read and send email in plain text format

An attacker may be able to exploit this vulnerability by convincing a user to open a specially crafted HTML email. Only reading email in plaintext will prevent exploitation of this vulnerability through email. Consider the security of fellow Internet users and send email in plain text format when possible.

If you use Microsoft Outlook, we encourage you to apply the Outlook Email Security Update. The update configures Outlook to open email messages in the Restricted Sites Zone, where Active scripting is disabled by default. In addition, the update provides further protection against malicious code that attempts to propagate via Outlook. The Outlook Email Security Update is available for Outlook 98 and Outlook 2000. The functionality of the Outlook Email Security Update is included in Outlook 2002 and Outlook Express 6. Outlook 2003 includes these and other security enhancements.

Configure Windows Explorer to use Windows Classic Folders

When Windows Explorer is configured to use the “Show common tasks in folders” option, HTML within a file may be processed when that file is selected. If the “Show common tasks in folders” is enabled, selecting a specially crafted HTML document in Windows Explorer may trigger this vulnerability. Note that the “Show common tasks in folders” is enabled by default. To mitigate this attack vector, enable the “Use Windows classic folders” option. To enable this option in Windows Explorer:

* Open Windows Explorer
* Select Folder Options from the Tools menu
* Select the "Use Windows classic folders" option in the Tasks section  

---

Vendor Information

416092

Filter by status: All Affected Not Affected Unknown

Filter by content: __ Additional information available

__ Sort by: Status Alphabetical

Expand all

Javascript is disabled. Click here to view vendors.

Microsoft Corporation __ Affected

Updated: September 27, 2006

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

Refer to <http://www.microsoft.com/technet/security/advisory/925568.mspx&gt; and <http://www.microsoft.com/technet/security/Bulletin/MS06-055.mspx&gt;.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%23416092 Feedback>).

CVSS Metrics

Group	Score	Vector
Base
Temporal
Environmental

References

• <http://www.microsoft.com/technet/security/Bulletin/MS06-055.mspx&gt;
• <http://sunbeltblog.blogspot.com/2006/09/seen-in-wild-zero-day-exploit-being.html&gt;
• <http://msdn.microsoft.com/workshop/author/vml/SHAPE/introduction.asp&gt;
• <http://www.microsoft.com/technet/security/advisory/925568.mspx&gt;

Acknowledgements

This vulnerability was reported by Sunbelt Software.

This document was written by Jeff Gennari.

Other Information

CVE IDs:	CVE-2006-4868
Severity Metric:	46.28 Date Public: