Mozilla Patches Firefox Bug from Pwn2Own Hacker Contest

Mozilla patches a Firefox vulnerability exploited at the CanSecWest Pwn2Own contest in March. Among Firefox, Internet Explorer, Apple Safari and Google Chrome, only Google's browser emerged from the contest unscathed.

Mozilla has patched the Firefox flaw exploited during the Pwn2Own contest at the CanSecWest security conference, held March 24 to 26.

The bug was discovered and exploited by a researcher from MWR InfoSecurity going by the hacker alias "Nils." According to Mozilla, the vulnerability was a memory corruption flaw. "By moving DOM nodes between documents, Nils found a case where the moved node incorrectly retained its old scope. If garbage collection could be triggered at the right time then Firefox would later use this freed object," allowing the possibility of code execution by an attacker, Mozilla said.

The vulnerability only affected Firefox 3.6 and not earlier versions of the browser, according to Mozilla. It is fixed in Firefox 3.6.3.

Nils exploited the issue on Windows 7 in his attack, circumventing the Address Space Layout Randomization and Data Execution Prevention features Microsoft has touted. In comments after the contest, Pete LePage, product manager of Microsoft's Internet Explorer developer division, noted that the features are intended to serve as additional layers of protection, not as full barriers to exploits.

"Recently, there has been some news from some security researchers about how they've managed to bypass DEP or ASLR in Internet Explorer ... Defense-in-depth techniques aren't designed to prevent every attack forever, but to instead make it significantly harder to exploit a vulnerability," LePage said in a March 26 blog post. "Defense in depth features, including DEP and ASLR continue to be highly effective protection mechanisms."

Internet Explorer 8 and Apple's Safari 4 browser were successfully exploited in the contest as well, though patches for those vulnerabilities have not been released. The only browser in the contest to emerge unscathed was Google Chrome 4.