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Mozilla Foundation Security Advisory 2008-16

Title: HTTP Referrer spoofing with malformed URLs
Impact: Moderate
Announced: March 25, 2008
Reporter: Gregory Fleischer, RSnake
Products: Firefox, SeaMonkey

Fixed in: Firefox
  SeaMonkey 1.1.9


Security researcher Gregory Fleischer demonstrated a problem with the HTTP Referer: (sic) header sent with requests to URLs containing Basic Authentication credentials with empty usernames. In these cases a number of leading characters, based on the length of the password in the URL, are removed from the referrer hostname. Fleischer pointed out that websites which only check the Referer: header to protect against Cross-Site Request Forgery (CSRF) could be attacked using this flaw. This concept was based on and expanded from a post to the forum by security researcher RSnake.