Mozilla announces fix for Firefox protocol handler flaw

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Mozilla on Wednesday pushed out a fix for a Firefox vulnerability that could be exploited to steal cookies and session history.

The bug, which affects the chrome protocol handler, was disclosed nearly two weeks ago by researcher Gerry Eisenhaur. He said on his hiredhacker.com blog that attackers could load malicious JavaScript onto a victim's machine, but Mozilla had only considered the possibility a low-risk threat.

On Tuesday, however, Window Snyder, Mozilla's security chief, said on her blog that Mozilla was raising the severity level to “high.” She admitted that hundreds of “flat” plug-ins are at risk. “Flat” add-ons do not store their contents in a JAR archive; therefore, their contents could permit attackers to read random files on the hard drive, according to Mozilla.

“The reason Mozilla bumped this up to high is because I released a PoC [proof of concept] that reads the sessionstore.js file,” Eisenhaur told SCMagazine.com Wednesday via instant messenger. “That exposes the user's current session [windows, history, cookies, etc.] to an attacker.”

He said the sessionstore.js file records open windows and users' histories and cookies.

“I think they didn't realize what data could be stolen, which is why I released the second demo,” Eisenhaur said.

While the issue reportedly was resolved today, Mozilla is not planning to push out a new version of Firefox, v. 2.0.0.12, which will contain the fix, until Tuesday.

But Eisenhaur said he thinks the patch may be flawed.

“I just read through it and I think I can still exploit the attack,” he said. “I am waiting for it to build now so I can verify.”
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