Mozilla Patches Firefox's Critical Pwn2Own Vulnerability

Firefox 3.0.8 was released several days earlier than expected. As recently as Thursday, Mozilla had set April 1 as the ship date for what the company labeled a "high-priority fire-drill security update" that would fix not only the Pwn2Own bug, but another that was revealed last Wednesday.

Both vulnerabilities were rated critical by Mozilla, But the most notable was clearly the one exploited earlier this month at CanSecWest, the Vancouver, British Columbia security conference that hosts the Pwn2Own hacking challenge.

At the contest, a 25-year-old computer science student from Germany who would only give his first name as Nils hacked Firefox and Safari on an Apple Inc. notebook, as well as Microsoft Corp.'s Internet Explorer 8 running on Windows 7. Nils was paid $5,000 for each successful exploit by 3Com Inc.'s TippingPoint, the Pwn2Own sponsor.

According to Mozilla, Nils' bug is in XUL, Mozilla's XML user interface markup language. In some cases, the "_moveToEdgeShift" tree method crashed Firefox; that crash could then "be used by an attacker to run arbitrary code on a victim's computer," Mozilla concluded.

Mozilla restricted access to additional information on the vulnerability by locking down Bugzilla, its bug tracking and management database, allowing only authorized users to view more information on the flaw.

Firefox 3.0.8 also patched a critical vulnerability that had gone public on the milw0rm.com exploit site last Wednesday. The bug allowed an attacker to crash Firefox by using malicious XSL code embedded on a Web site. "An attacker could potentially use this crash to run arbitrary code on a victim's computer," Mozilla warned in the accompanying security advisory.

The new version of Firefox can be downloaded for Windows, Mac OS X and Linux from the Mozilla site. Current users can also call up their browsers' built-in updater, or wait for the automatic update notification, which should pop up within 48 hours.

As expected, Mozilla beat rivals Microsoft and Apple Inc. by patching its Pwn2Own vulnerability first. Although the exploit Nils used to hack IE8 Release Candidate 1 (RC1) has been blocked by the final version of the browser -- it shipped a day after Pwn2Own -- the underlying flaw has not been fixed, and can be leveraged by attackers against Windows XP, according to TippingPoint's manager of security response, Terri Forslof.