Public Vulnerability Reports

Microsoft Windows 2000 Agent URL Canonicalizing Stack Based Buffer Overflow Vulnerability

09.11.07

BACKGROUND

Microsoft Agent allows websites and programs to display animated characters that speak and move around the screen. The Microsoft Office "Clippy" character, the animated paper clip, is an example of a Microsoft agent character.

Agents can be created through the web browser by loading and interacting with an ActiveX control. Once this control is loaded it will start the Agent Service process, and pass requests from the browser to the service. More information can be found at the following site.

http://www.microsoft.com/msagent/default.asp

DESCRIPTION

Remote exploitation of a stack based buffer overflow vulnerability in Microsoft Corp's Microsoft Windows 2000 Agent service could allow an attacker to execute arbitrary code with the privileges of the logged in user.

The vulnerability exists within the Agent Service (agentsvr.exe). Due to improper handling of specially crafted URLs, an attack can cause stack based buffer overflow.

ANALYSIS

Exploitation of this vulnerability results in arbitrary code execution with the privileges of the logged in user. To exploit this vulnerability, an attacker would have to use social engineering techniques to convince a user to visit a malicious website. No further interaction is needed.

With default settings, Microsoft Outlook and Outlook Express can not be used to directly exploit this vulnerability. By default, Outlook and Outlook Express both run in Restricted mode which prevents Active Content from being loaded. However, an attacker could send an e-mail with a link to a malicious website. By following this link a user is susceptible to exploitation through the browser.

DETECTION

iDefense has confirmed the existence of this vulnerability in the Agent service included in Windows 2000. Microsoft reports that newer versions of the Agent service are not vulnerable.

WORKAROUND

Setting the kill bit for the following CLSID will prevent the control from loading in the browser:

{D45FD31B-5C6E-11D1-9EC1-00C04FD7081F}

This will not fix the vulnerability, but it will prevent it from being exploited through the web browser.

VENDOR RESPONSE

Microsoft has addressed this vulnerability within MS07-051. For more information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/Bulletin/MS07-051.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-3040 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

07/09/2007 Initial vendor notification
07/09/2007 Initial vendor response
09/11/2007 Coordinated public disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 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.