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Mozilla Foundation Security Advisory 2009-29

Title: Arbitrary code execution using event listeners attached to an element whose owner document is null
Impact: Critical
Announced: June 11, 2009
Reporter: moz_bug_r_a4
Products: Firefox, Thunderbird, SeaMonkey

Fixed in: Firefox 3.0.11
  SeaMonkey 1.1.17


Mozilla security researcher moz_bug_r_a4 reported that the owner document of an element can become null after garbage collection. In such cases, event listeners may be executed within the wrong JavaScript context. An attacker could potentially use this vulnerability to have a malicious event handler execute arbitrary JavaScript with chrome privileges.

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