Cross-Domain Redirect Vulnerability in Internet Explorer
A cross-domain vulnerability in Internet Explorer (IE) could allow an attacker to execute arbitrary code with the privileges of the user running IE.
There is a cross-domain vulnerability in the way IE determines the security zone of a browser frame that is opened in one domain then redirected by a web server to a different domain. A complex set of conditions is involved, including a delayed HTTP response (3xx status code) to change the content of the frame to the new domain. Vulnerability Note VU#713878 describes this vulnerability in more technical detail and will be updated as further information becomes available.
Other programs that host the WebBrowser ActiveX control or use the MSHTML rendering engine, such as Outlook and Outlook Express, may also be affected.
By convincing a victim to view an HTML document (web page, HTML email), an attacker could execute script in a different security domain than the one containing the attacker's document. By causing script to be run in the Local Machine Zone, the attacker could execute arbitrary code with the privileges of the user running IE.
Publicly available exploit code exists for this vulnerability, and US-CERT has monitored incident reports that indicate that this vulnerability is being actively exploited.
Microsoft has released a cumulative patch (867801) in Security Bulletin MS04-025 which addresses this issue.
Disable Active scripting and ActiveX controls
Disabling Active scripting and ActiveX controls in the Internet Zone (or any zone used by an attacker) appears to prevent exploitation of this vulnerability. Disabling Active scripting and ActiveX controls in the Local Machine Zone will prevent widely used payload delivery techniques from functioning. Instructions for disabling Active scripting in the Internet Zone can be found in the Malicious Web Scripts FAQ. See Microsoft Knowledge Base Article 833633 for information about securing the Local Machine Zone. Also, Service Pack 2 for Windows XP (currently at RC1) includes these and other security enhancements for IE.
Do not follow unsolicited links
Do not click on unsolicited URLs received in email, instant messages, web forums, or internet relay chat (IRC) channels. While this is generally good security practice, following this behavior will not prevent exploitation of this vulnerability in all cases.
Maintain updated anti-virus software
Anti-virus software with updated virus definitions may identify and prevent some exploit attempts. Variations of exploits or attack vectors may not be detected. Do not rely solely on anti-virus software to defend against this vulnerability.
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