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There’s a zero-day exploit in the wild that’s being used to execute malicious code on the computers of people using Tor and possibly other users of the Firefox browser, officials of the anonymity service confirmed Tuesday.
Word of the previously unknown Firefox vulnerability first surfaced in this post on the official Tor website.
According to security researchers who analyzed the code, it exploits a memory corruption vulnerability that allows malicious code to be executed on computers running Windows.
The malicious payload it delivers, according to an independent researcher who goes by the Twitter handle @TheWack0lian, is almost identical to one that was used in 2013 to deanonymize people visiting a Tor-shielded child pornography site.
The FBI ultimately acknowledged responsibility for the exploit, which was embedded in Web pages served by a service known as Freedom Hosting.
“It’s basically almost EXACTLY the same as the payload used in 2013,” TheWack0lian told Ars. “It exploits some vuln that executes code very similar to that used in the 2013 Tor browser exploit. Most of the code is identical, just small parts have changed.”
Analysis of the 2013 attack is here. Where that attack sent a unique identifier to a server located at the IP address of 184.108.40.206, the new one sends data to a server at 220.127.116.11.
The latter IP address is assigned to French Web host OVH.
It wasn’t responding to queries at the time this post was being prepared.
The versions span from 41 to 50, with version 45 ESR being the version used by the latest version of the Tor browser.
The adjustments are an indication that the people who developed the attack tested it extensively to ensure it worked on multiple releases of Firefox.
The exploit makes direct calls to kernel32.dll, a core part of the Windows operating system.
This post will be updated in the coming hours in the event important new details become available.