Mozilla has confirmed it will patch a critical vulnerability in the newest version of Firefox by the end of the month.
Although the patch won't be added to Firefox before this week's Pwn2Own browser hacking challenge, researchers won't be allowed to use the flaw, according to the contest's organiser.
"The vulnerability was determined to be critical and could result in remote code execution by an attacker," Mozilla acknowledged in a post to its security blog.
"The vulnerability has been patched by developers and we are currently undergoing quality assurance testing for the fix."
Firefox 3.6, which Mozilla launched in January, is affected, Mozilla said, adding that it would be patched in version 3.6.2, currently slated to ship on March 30.
The bug was disclosed by Russian researcher Evgeny Legerov a month ago in a message posted on a forum hosted by Immunity, the developer best known for its Canvas penetration testing framework.
Legerov works for Intevydis, which produces the VulnDisco add-on for Canvas.
Legerov did not publish attack code, and initially refused to provide details to Mozilla, according to a March 4 entry he posted on his blog.
"I've ignored emails ... from Mozilla, please do not waste my and your time anymore," Legerov wrote.
The blog has since been deleted, but is still available via Google's cache.
In comments appended to a vulnerability alert published by Danish bug tracker Secunia, several users questioned Legerov's motives for making the announcement, while others chided Secunia for not thoroughly testing the flaw or claimed that it was all a hoax.
Mozilla said Legerov had eventually sent them "sufficient details to reproduce and analyse the issue".
Until the March 30 patch is released, users can upgrade Firefox to the beta of version 3.6.2, which includes the fix, by downloading the preview .
Although Apple and Google have recently updated Safari and Chrome, respectively - beefing up the browsers' security before the $100,000 Pwn2Own hacking contest starts on March 24 - the version of Firefox that will be used in the challenge will lack the patch for Legerov's vulnerability.
Pwn2Own will pit only production versions of Chrome, Firefox, Internet Explorer (IE) and Safari against the hacking talents of researchers.
However, that doesn't mean hackers will be able to use the bug to claim one of the $10,000 prizes for successfully exploiting Firefox.
"We will have our entire research team on-site so that we can do our best to ensure that known issues such as this one do not turn up at our contest," said Aaron Portnoy, a research team lead with 3Com TippingPoint, the company sponsoring Pwn2Own.
Portnoy, who organised the fourth annual contest, has predicted that Microsoft 's IE8 will be the first browser to fall during the three-day event.
Mozilla will also patch Firefox 3.0 (with 3.0.19) and Firefox 3.5 (with 3.5.9) on March 30.
Firefox 3.0.19 will be the final security update for the browser Mozilla debuted in mid-2008.
See also: Tweaked Firefox offers 3D graphics