Mozilla Foundation Security Advisory 2008-34

Remote code execution by overflowing CSS reference counter

July 15, 2008
TippingPoint Zero Day Initiative
Firefox, SeaMonkey, Thunderbird
Fixed in
  • Firefox
  • Firefox 3.0.1
  • SeaMonkey 1.1.11
  • Thunderbird


An anonymous researcher, via TippingPoint's Zero Day Initiative program, reported a vulnerability in Mozilla's internal CSSValue array data structure. The vulnerability was caused by an insufficiently sized variable being used as a reference counter for CSS objects. By creating a very large number of references to a common CSS object, this counter could be overflowed which could cause a crash when the browser attempts to free the CSS object while still in use. An attacker could use this crash to run arbitrary code on the victim's computer.

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.


Disable JavaScript until a version containing these fixes can be installed.


Bug details embargoed until after the upgrade period