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Mozilla Foundation Security Advisory 2008-63

Title: User tracking via XUL persist attribute
Impact: Low
Announced: December 16, 2008
Reporter: Hish
Products: Firefox

Fixed in: Firefox 3.0.5


Security researcher Hish reported that the persist attribute in XUL elements can be used to store cookie-like information on a user's computer which could later be read by a website. This creates a privacy issue for users who have a non-standard cookie preference and wish to prevent sites from setting cookies on their machine. Even with cookies turned off, this issue could be used by a website to write persistent data in a user's browser and track the user across browsing sessions. Additionally, this issue could allow a website to bypass the limits normally placed on cookie size and number.