Software Engineering Institute

The Cross-Domain Security Model

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 which zone or domain a URL exists in 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.
The problem

Microsoft Internet Explorer is vulnerable to a cross-domain violation. When a source element is used in combination with a redirect, a web site in one domain has the ability to access information in another domain or zone.

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 may be able to execute script in the Local Machine Zone. Script that executes in the Local Machine Zone can be used to download and execute arbitrary code. An attacker may obtain full access to web content in another domain, which may reside in a different security zone. The impact is similar to that of a cross-site scripting vulnerability. This includes the ability to spoof or modify web content, access website information such as cookies, or retrieve data from an encrypted HTTPS connection. For a more detailed description of the impact of cross-site scripting vulnerabilities, please see CERT Advisory CA-2000-02.

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

Disable Active Scripting

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