Software Engineering Institute

Mozilla uses a same origin 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. From the same origin policy:

Mozilla considers two pages to have the same origin if the protocol, port (if given), and host are the same for both pages.
Mozilla can evaluate script contained in a URI. For example, either of the following URIs will display an alert dialog containing the text "Hello world.":

javascript:eval('alert("Hello world.")')

javascript:alert("Hello world.")

This URI will display an alert dialog with the contents of the HTTP cookie for the current site:

javascript:alert(document.cookie)

The same origin security model should not allow script from one domain to read or modify data in a different domain using this type of "script URI".

Mozilla does not properly validate the source domain of some URIs stored in the browser history. Script in a URI stored in the history can be executed in the context of a different domain. An attacker can create a javascript: URI containing eval(), cause the user to visit a web site in a different domain, and then programmatically cause the web browser to return to the previous javascript: page to trigger the cross-domain violation. The violation will also occur if the user manually clicks the "Back" button to return to the javascript: page.

In limited testing, Firefox 1.0.3 and Mozilla 1.7.7 are vulnerable. Previous versions do not appear to be vulnerable.

By convincing a victim to view an HTML document (web page), an attacker could evaluate script in a different security domain than the one containing the attacker's document. The attacker could read or modify data in other web sites (read cookies/content, modify/create content, etc.). If the script is evaluated with chrome privileges, an attacker could execute arbitrary commands on the user's system. VU#648758 describes one way to execute script with chrome privileges. However, due to recent changes made to the addons.mozilla.org and update.mozilla.org sites, the current proof-of-concept code that utilizes VU#648758 no longer functions properly.

Upgrade
This issue is resolved in Firefox 1.0.4 and Mozilla 1.7.8.

Workarounds

Disable JavaScript

Disable JavaScript in your browser's preferences. Instructions for disabling JavaScript can be found in the Malicious Web Scripts FAQ.