Source: Collection Chrisophel via Alamy Stock Photo

For a brief window of time in October, Russian hackers had the ability to launch arbitrary code against anyone in the world using Firefox or Tor.

On Oct. 8, researchers from ESET first spotted malicious files on a server managed by the Russian advanced persistent threat (APT) RomCom (aka Storm-0978, Tropical Scorpius, UNC2596). The files had gone online just five days earlier, on Oct. 3. Analysis showed that they leveraged two zero-day vulnerabilities: one affecting Mozilla software, the other Windows. The result: an exploit that spread the RomCom backdoor to anyone who visited an infected website, no clicks required.

Luckily, both issues were remediated quickly. "The attackers only had a really small window to try to compromise computers," explains Romain Dumont, malware researcher with ESET. "Yes, there was a zero-day vulnerability. But, still, it was patched really fast."

Dark Reading has reached out to Mozilla for comment on this story.

A Zero-Day in Firefox & Tor

The first of the two vulnerabilities, CVE-2024-9680, is a use-after-free opportunity in Firefox animation timelines — the browser mechanism that handles how animations play out based on user interactions with websites. Its power to afford attackers arbitrary command execution earned it a "critical" 9.8 rating from the Common Vulnerability Scoring System (CVSS). 

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Importantly, CVE-2024-9680 affects more than just Firefox. Mozilla's open source email client "Thunderbird" is also impacted, as is the ultrasecretive Tor browser, which is built from a modified version of Firefox's Extended Support Release (ESR) browser.

In October, RomCom deployed specially crafted websites that would instantly trigger CVE-2024-9680 without the need for any victim interaction. Victims would unknowingly download the RomCom backdoor from RomCom-controlled servers, then quickly be redirected to the original website they thought they were visiting all along.

These malicious domains were made to mimic the real sites associated with the ConnectWise and Devolutions IT services platforms, and Correctiv, a nonprofit newsroom for investigative journalism in Germany. That these organizations are both political and economic in nature might not surprise those familiar with RomCom, which has always conducted opportunistic cybercrime, but in more recent times has added politically motivated espionage to its agenda. Its activity in 2024 has included campaigns against the insurance and pharmaceutical sectors in the US, but also the defense, energy, and government sectors in Ukraine.

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It's unclear by what means of social engineering RomCom might have spread these malicious sites.

What We Know of RomCom's Campaign

Not content with only running code in a victim's browser, however, RomCom also employed a second vulnerability, CVE-2024-49039. This high-severity 8.8 CVSS-rated bug in the Windows Task Scheduler allows for privilege escalation, thanks to an undocumented remote procedure calls (RPC) endpoint unintentionally accessible to low level users. In this case, RomCom used CVE-2024-49039 to escape the browser sandbox and onto a victim's machine at large.

The damage that might've been done with such a powerful exploit chain, and exactly who was affected by it last month, remains unknown. What's clear at this point is that the overwhelming majority of targets were located in North America and Europe — particularly the Czech Republic, France, Germany, Poland, Spain, Italy, and the US — plus scattered victims in New Zealand and French Guiana.

Also, notably, none of the victims tracked by ESET were compromised via Tor. "Tor has some predefined settings that differ from Firefox, so maybe it would not have worked," Damien Schaeffer, senior malware researcher at ESET speculates. He notes, too, that RomCom's primary targets appeared to be corporations, which rarely use Tor.

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Both CVE-2024-9680 and CVE-2024-49039 have since been patched — the former on Oct. 9, just 25 hours after Mozilla was notified of the issue, and the latter on Nov. 12.

"By now, I hope, the problem is more or less done," Schaeffer says. Still, for any given organization, "It'll depend on their policies. If you have good patch management, this would have been fixed in one day or so. But it's up to people to fix their stuff."