Software Engineering Institute

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.

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.

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.