July 23, 2007

Password vulnerability in Firefox

Author: Joe Barr

According to a message posted over the weekend on the Full-Disclosure mailing list, the latest version of Firefox,, contains a password management vulnerability that can allow malicious Web sites to steal user passwords. If you have JavaScript enabled and allow Firefox to remember your passwords, you are at risk from this flaw.

The Mozilla team fixed a similar flaw last November, one which did not require JavaScript. The heise Security Web site contains a demo/proof of concept of the vulnerability risk that you can use to determine your vulnerability.

The original flaw was referred to as reverse cross-site scripting and was reportedly widely used on Myspace.com.

Note: A reader has pointed out that MySpace.com does not allow Javascript, as originally reported. The reader is correct, although there do seem to be workarounds which result in Javascript executing on some browsers.

Discussions between heise Security and Mozilla developers describe a debate among Mozilla developers over removing this feature, since "evil" server pages can steal passwords from browsers whether the user has opted for password management by Firefox or not.

Apple's Safari is vulnerable in the same way. Current workarounds include disabling JavaScript in Firefox or avoiding the use of Firefox password management on sites where users are allowed to post JavaScript pages.


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