Mozilla Foundation Security Advisory 2009-17

Same-origin violations when Adobe Flash loaded via view-source: scheme

April 21, 2009
Gregory Fleischer
Firefox, SeaMonkey, Thunderbird
Fixed in
  • Firefox 3.0.9
  • SeaMonkey 1.1.17
  • Thunderbird


Security researcher Gregory Fleischer reported that when an Adobe Flash file is loaded via the view-source: scheme, the Flash plugin misinterprets the origin of the content as localhost, leading to two specific vulnerabilities:

  1. The Flash file can bypass restrictions imposed by the crossdomain.xml mechanism and initiate HTTP requests to arbitrary third-party sites. This vulnerability could be used by an attacker to perform CSRF attacks against these sites.
  2. The Flash file, being treated as a local resource, can read and write Local Shared Objects on a user's machine. This vulnerability could be used by an attacker to place cookie-like objects on a user's computer and track them across multiple sites.

Additonally, Fleischer reported that the jar: protocol could be used to bypass restrictions normally preventing content loaded via view-source: from being rendered.

Thunderbird shares the browser engine with Firefox and could be vulnerable if plugins were to be enabled in mail. This is not the default setting and we strongly discourage users from enabling plugins in mail.