Software Engineering Institute

IE uses a cross-domain security model to maintain separation between browser frames from different sources. This model is designed to prevent code in one domain from accessing data in a different domain. The Internet Security Manager Object determines in which zone or domain a URL exists and what actions can be performed. From Microsoft Security Bulletin MS03-048:

One of the principal security functions of a browser is to ensure that browser windows that are under the control of different Web sites cannot interfere with each other or access each other's data, while allowing windows from the same site to interact with each other. To differentiate between cooperative and uncooperative browser windows, the concept of a "domain" has been created. A domain is a security boundary - any open windows within the same domain can interact with each other, but windows from different domains cannot. The cross-domain security model is the part of the security architecture that keeps windows from different domains from interfering with each other.
Internet Explorer 6 fails to properly enforce the cross-domain security model when a page location is modified through use of an object, rather than a string.

Proof-of-concept code that demonstrates this vulnerability is publicly available.

By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message), an attacker may be able to obtain access to web content in another domain. The impact is similar to that of a cross-site scripting vulnerability. For a more detailed description of the impact of cross-site scripting vulnerabilities, please see CERT Advisory CA-2000-02.

We are currently unaware of a practical solution to this problem. Please consider the following workarounds:

Apply an update

This vulnerability does not appear to affect Internet Explorer 7. Therefore, updating to Internet Explorer 7 may mitigate this vulnerability.

Disable Active Scripting

This vulnerability can be mitigated by disabling Active Scripting, as specified in the "Securing Your Web Browser" document.