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Hackers: Firefox has JavaScript flaw

Hackers: Firefox has JavaScript flaw
Hackers: Firefox has JavaScript flaw,39020369,39283751,00.htm 

By Joris Evers
October 02, 2006

Mozilla is investigating claims that its Firefox browser is vulnerable 
to a zero-day attack

The open source Firefox Web browser is critically flawed in the way it 
handles JavaScript, two hackers said on Saturday afternoon.

An attacker could commandeer a computer running the browser simply by 
crafting a Web page that contains some malicious JavaScript code, Mischa 
Spiegelmock and Andrew Wbeelsoi said in a presentation at the ToorCon 
hacker conference in San Diego. The flaw affects Firefox on Windows, 
Apple's Mac OS X and Linux, they said.

"Internet Explorer, everybody knows, is not very secure. But Firefox is 
also fairly insecure," said Spiegelmock, who in everyday life works at 
blog company SixApart. He detailed the flaw, showing a slide that 
displayed key parts of the attack code needed to exploit it.

The flaw is specific to Firefox's implementation of JavaScript, a 
10-year-old scripting language widely used on the Web. In particular, 
various programming tricks can cause a stack overflow error, Spiegelmock 
said. The implementation is a "complete mess," he said. "It is 
impossible to patch."

The JavaScript issue appears to be a real vulnerability, Window Snyder, 
Mozilla's security chief, said after watching a video of the 
presentation Saturday night. "What they are describing might be a 
variation on an old attack," she said. "We're going to do some 

Snyder said she isn't happy with the disclosure and release of an 
apparent exploit during the presentation. "It looks like they had enough 
information in their slide for an attacker to reproduce it," she said. 
"I think it is unfortunate because it puts users at risk, but that seems 
to be their goal."

At the same time, the presentation probably gives Mozilla enough data to 
fix the apparent flaw, Snyder said. However, because the possible flaw 
appears to be in the part of the browser that deals with JavaScript, 
addressing it might be tougher than the average patch, she added. "If it 
is in the JavaScript virtual machine, it is not going to be a quick 
fix," Snyder said.

The hackers claim they know of about 30 unpatched Firefox flaws. They 
don't plan to disclose them, instead holding on to the bugs.

Jesse Ruderman, a Mozilla security staffer, attended the presentation 
and was called up on the stage with the two hackers. He attempted to 
persuade the presenters to responsibly disclose flaws via Mozilla's bug 
bounty program instead of using them for malicious purposes such as 
creating networks of hijacked PCs, called botnets.

"I do hope you guys change your minds and decide to report the holes to 
us and take away $500 per vulnerability instead of using them for 
botnets," Ruderman said.

The two hackers laughed off the comment. "It is a double-edged sword, 
but what we're doing is really for the greater good of the Internet, 
we're setting up communication networks for black hats," Wbeelsoi said.

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