Original URL: http://www.theregister.co.uk/2013/08/06/tor_fingers_firefox_for_fail/

Tor fingers Firefox flaw for FAIL but FBI's also in the frame

Malware means 'attacker now has a list of vulnerable Tor users'

By Simon Sharwood

Posted in Security, 6th August 2013 02:02 GMT

Tor has confirmed the existence of malware that has taken down some of its hidden nodes - and says flaws in Firefox are at the heart of the problem.

The network anonymising service yesterday noted the disappearance of some nodes on its network. The outfit hasn't offered any more insight into what's down, or exactly what brought down anything that is offline.

But it has issued a ”critical security announcement saying Tor Browser Bundle versions based on Firefox 17 ESR are vulnerable to “arbitrary code execution” that means “an attacker could in principle take over the victim's computer”.

The news gets worse, as Tor also says:

“However, the observed version of the attack appears to collect the hostname and MAC address of the victim computer, send that to a remote webserver over a non-Tor connection, and then crash or exit. The attack appears to have been injected into (or by) various Tor hidden services, and it's reasonable to conclude that the attacker now has a list of vulnerable Tor users who visited those hidden services.”

That last sentence has tongues wagging, because rumblings about inaccessible Tor nodes started to appear not long after the FBI cuffed a man suspected of using Tor hidden services to distribute child pornography.

There's no clear link between the two incidents, but plenty of folk are doing so and imagining weaponised malware that targets Tor users, seeks out hidden services, tries to crash their web servers and compiles a list of TOr users. Reverse engineer and secruity researcher Vlad Tsyrklevich has said as much in this analysis, while others have traced the malware back to a defence contractor.

Avoiding the flaw is easy. Firefox 17.0.7 ESR addressed the bug. Firefox is now on release 22, so if you have upgraded, you're safe. Tor Browser bundles 2.3.25-10, 2.4.15-alpha-1, 2.4.15-beta-1 and 3.0alpha2 all offer a fix. ®