Software Engineering Institute

A regular expression is a special text string for describing a search pattern. The JavaScript interpreter in the Mozilla browser and derived products includes the ability to process regular expressions. An integer overflow vulnerability has been discovered in the way that some versions of these products handle and overly large regular expression. According to Mozilla Foundation Security Advisory 2006-11:

As part of the Firefox 1.5 release we fixed several crash bugs to improve the stability of the product. Some of these crashes showed evidence of memory corruption that we presume could be exploited to run arbitrary code and have been applied to the Firefox 1.0.x and Mozilla Suite 1.7.x releases
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Alden D'Souza reported a crash when using an extremely large regular expression in JavaScript. This was tracked down to a 16-bit integer overflow that could potentially cause the browser to interpret attacker supplied data as JavaScript bytecode.
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Note: 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.

Remote attackers may be able to crash a vulnerable program or run code of their choosing on an affected system. The attacker-supplied code would be executed with the permissions of the user running the vulnerable program.

Upgrade

The Mozilla Foundation has published Mozilla Foundation Security Advisory 2006-11 in response to this issue. Users are encouraged to review this advisory and upgrade to the fixed versions of the products it describes.

Workarounds

Users, particularly those who are unable to upgrade to a fixed version of the software, are encouraged to disable JavaScript in the affected programs.