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 fails to properly handle location.hostname parameters that have embedded null characters, which can cause a cross-domain violation. Note that this only affects web sites that have specify the document.domain setting for relaxed same origin protection. This vulnerability appears to affect all Mozilla-based browsers, including Firefox.

By convincing a victim to view an HTML document (web page), an attacker could modify data in another domain. For example, web page script in one domain could set a cookie for a web page in another domain.

Apply an update
This vulnerability is addressed in Firefox 2.0.0.2, Firefox 1.5.0.10, and SeaMonkey 1.0.8, as specified in MFSA 2007-07.

Disable the ability to set location.hostname

This vulnerability can be mitigated by disabling the ability for a web site to set the location.hostname property. This can be accomplished by adding the following line to the user.js file:

user_pref("capability.policy.default.Location.hostname.set", "noAccess");