Mozilla and Tor recently released patches for the Firefox browser as well as the Firefox-based Tor browser aiming to block a recent attack. This attack exploited a Firefox animation remote code execution flaw to unmask users of the Tor anonymity network.
Though it’s seen that the payload works against Windows systems that run Firefox browser and the Tor browser, there were also reports of the vulnerability being there on Firefox for Mac OS and Linux and hence users were promptly made to update their browsers on these platforms.
Mozilla’s release describes the vulnerability in brief- “A use-after-free vulnerability in SVG Animation has been discovered. An exploit built on this vulnerability has been discovered in the wild targeting Firefox and Tor Browser users on Windows.” The Mozilla release, dated November 30, rates it as critical and says that it is fixed in Firefox version 50.0.2, Firefox Extended Support Release version 45.5.1 and Mozilla’s Thunderbird email client version 45.5.1.
A Tor release, dated November 30, states- “Tor Browser 6.0.7 is now available from the Tor Browser Project page and also from our distribution directory. This release features an important security update to Firefox and contains, in addition to that, an update to NoScript (126.96.36.199).
The security flaw responsible for this urgent release is already actively exploited on Windows systems. Even though there is currently, to the best of our knowledge, no similar exploit for OS X or Linux users available the underlying bug affects those platforms as well. Thus we strongly recommend that all users apply the update to their Tor Browser immediately. A restart is required for it to take effect.”
Mozilla’s security lead, Daniel Veditz dwells on another aspect of the zero day exploit in a post made in the Mozilla Security Blog. He says- “The exploit in this case works in essentially the same way as the “network investigative technique” used by FBI to deanonymize Tor users (as FBI described it in an affidavit). This similarity has led to speculation that this exploit was created by FBI or another law enforcement agency. As of now, we do not know whether this is the case. If this exploit was in fact developed and deployed by a government agency, the fact that it has been published and can now be used by anyone to attack Firefox users is a clear demonstration of how supposedly limited government hacking can become a threat to the broader Web.”