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Mozilla Foundation Security Advisory 2006-19

Title: Cross-site scripting using .valueOf.call()
Impact: High
Date: April 13, 2006
Reporter: moz_bug_r_a4
Products: Firefox, Thunderbird, Mozilla Suite

Fixed in: Firefox 1.5
  Firefox 1.0.8
  Thunderbird 1.5
  Thunderbird 1.0.8
  SeaMonkey 1.0
  Mozilla Suite 1.7.13

Description

moz_bug_r_a4 discovered that .valueOf.call() and .valueOf.apply() when called with no arguments were returning the Object class prototype rather than the caller's global window object. When called on a reachable property of another window this provides a hook to get around the same-origin protection, allowing an attacker to inject script into another window.

Cross-site script injection can be used to steal confidential data such as cookies or passwords, or perform actions on the user's behalf. It can also be used to alter the content of the other window which could be used to fool a user into trusting bogus information or downloaded content.

Thunderbird shares the JavaScript 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.

Workaround

Disable JavaScript until a fixed version can be installed.

References

Exploit code and details embargoed during the active update period.