Software Engineering Institute

Microsoft Internet Explorer does not properly handle requests to mismatched DOM objects, such as the window() object. When an HTML document references a DOM object in a specially crafted manner, Internet Explorer can crash in a way that allows an attacker to execute arbitrary shell code.

Note: Proof of concept code is publicly available. This vulnerability is being actively exploited to spread malicious software such as Win32/Delf.DH and Troj/Clunky-B.

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

Apply an update
Apply the appropriate update, as specified in Microsoft Security Bulletin MS05-054.

Disable Active scripting

Disabling Active scripting in the Internet Zone (or any zone used by an attacker) appears to prevent exploitation of this vulnerability. Instructions for disabling Active scripting in the Internet Zone can be found in the Malicious Web Scripts FAQ. Microsoft has provided this and other workarounds in Microsoft Security Advisory 911302 and Microsoft Security Bulletin MS05-054.

Note that disabling Active scripting in the Internet Zone will reduce the functionality of some web sites.

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.