Vulnerability Note VU#262004

Microsoft Internet Explorer fails to properly handle chained Cascading Style Sheets

Overview

Microsoft Internet Explorer fails to properly handle chained Cascading Style Sheets (CSS). This can allow a remote attacker to execute arbitrary code on a vulnerable system.

I. Description

CSS is a mechanism for adding style to web documents. Microsoft Internet Explorer contains a vulnerability in the handling of chained CSS. An attacker can exploit this vulnerability by creating a specially crafted HTML document that causes memory corruption when it is viewed with Internet Explorer.

II. Impact

By convincing a user to view a specially crafted HTML document (e.g., a web page, an HTML email message, or an email attachment), an attacker could execute arbitrary code with the privileges of the user. The attacker could also cause Internet Explorer (or the program using the WebOC control) to crash.

III. Solution

Apply an update

This vulnerability is addressed in Microsoft Security Bulletin MS06-042.

Note that this patch may cause problems for certain users. Per Microsoft Knowledgebase Article 923762:

Consider the following scenario. You run Microsoft Internet Explorer 6 Service Pack 1 (SP1) on a computer that is running Microsoft Windows XP with Service Pack (SP1) or Microsoft Windows 2000 with Service Pack 4 (SP4). You install the Internet Explorer cumulative security update that is documented in Microsoft Knowledge Base article 918899. In this scenario, Internet Explorer unexpectedly exits when you view a Web site that uses the HTTP 1.1 protocol and compression.

Disable Active Scripting

This vulnerability can be mitigated by disabling Active Scripting, as specified in the "Securing Your Web Browser" document. Although this does not remove the vulnerability, it does block known attack vectors.

Systems Affected

Vendor	Status	Date Notified	Date Updated
Microsoft Corporation	Vulnerable	8-Aug-2006

References

http://www.microsoft.com/technet/security/bulletin/ms06-042.mspx
http://www.us-cert.gov/reading_room/securing_browser/#Internet_Explorer
http://www.w3.org/Style/CSS/
http://secunia.com/advisories/21396/

Credit

This vulnerability was reported by Microsoft, who in turn credit Sam Thomas.

This document was written by Will Dormann.

Other Information

Date Public:	2006-08-08
Date First Published:	2006-08-08
Date Last Updated:	2006-08-16
CERT Advisory:
CVE-ID(s):	CVE-2006-3451
NVD-ID(s):	CVE-2006-3451
US-CERT Technical Alerts:
Metric:	20.25
Document Revision:	7

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Produced 2006 by US-CERT, a government organization
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