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Mozilla Foundation Security Advisory 2005-36

Title: Cross-site Scripting through global scope pollution
Severity: High
Reporter: shutdown
Products: Firefox, Mozilla Suite

Fixed in: Firefox 1.0.3
  Mozilla Suite 1.7.7

Description

As you browse from site to site each new page should start with a clean slate. shutdown reports a technique that pollutes the global scope of a window in a way that persists from page to page. A malicious script could define a setter function for a variable known to be used by a popular site, and if the user does browse to that site the malicious script will run in that page. This would allows the setter script to steal cookies or the contents of the page, or potentially perform actions on the user's behalf (such as make purchases or delete webmail) depending heavily on how the site was designed.

The objects persist until the window or tab is closed.

Workaround

Open a new window or tab before going to any site requiring a log in or containing sensitive information. Or disable javascript.

References