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Unpatched Firefox 1.5 exploit made public

A flaw in the open-source browser's history.dat file potentially puts users at risk of a DoS attack.

A correction was made to this story. Read below for details.

Exploit code for the latest version of open-source browser Firefox was published Wednesday, potentially putting users at risk of a denial-of-service attack.

The exploit code takes advantage of a bug in the recently released Firefox 1.5, running on Windows XP with Service Pack 2. Firefox, which initially debuted over a year ago, has moved swiftly to capture 8 percent of the browser market.

The latest Firefox flaw exists in the history.dat file, which stores information from Web sites users have visited with the Firefox 1.5 browser, according to a posting on the Internet Storm Center, which monitors online threats.

"If the topic of a page is crafted to be long enough, it will crash the browser each time it is started after going to such a page," according to the Internet Storm Center posting. "Once this happens, Firefox will be unable to be started until you erase the history.dat file manually."

In testing Firefox 1.5 without a system running McAfee security software, the Firefox 1.5 browser would stall and not respond to a user's mouse, said Johannes Ullrich, chief research officer for the Sans Institute, which runs the Internet Storm Center.

"Users have to kill out of the browser and start over again. This stalled browser creates a DOS (denial of service) condition," Ullrich said.

The author of the proof-of-concept exploit code, initially published by nonprofit group Packet Storm, claimed the glitch is a buffer overflow that could lead to a denial-of-service attack and may even be used for a malicious execution of code. Packet Storm itself said a possible denial-of-service condition exists.

Ullrich, however, said while the potential may exist, it has not been proven either way that malicious code could be executed.

The Mozilla Foundation, which released Firefox, said it was not able to confirm the browser would crash or be at risk of a DOS attack, after visiting certain Web sites. And Mozilla has not received any reports from users of such a problem, said Mike Schroepfer, vice president of engineering for Mozilla Corp.

He added that Firefox 1.5 can be slugglish on its next start-up, due to a bug in the history.dat, but it is not a security problem.

"We have gotten no independent verification that it crashes (Firefox), but there have been a lot of attempts to try," Schroepfer said.

Correction: This story incorrectly stated the affiliation of Mike Schroepfer. It also misstated Mozilla's results in verifying the Firefox 1.5 flaw. The problem itself was not a security vulnerability but actually a flaw in the browser, according to Mozilla. In addition, it misstated PacketStorm's assessment of the situation.