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‘ArcaneDoor’ Cyberspies Hacked Cisco Firewalls to Access Government Networks

May 15, 2024

 Source : Andy Greenberg via


Network security appliances like firewalls are meant to keep hackers out. Instead, digital intruders are increasingly targeting them as the weak link that lets them pillage the very systems those devices are meant to protect. In the case of one hacking campaign over recent months, Cisco is now revealing that its firewalls served as beachheads for sophisticated hackers penetrating multiple government networks around the world.

On Wednesday, Cisco warned that its so-called Adaptive Security Appliances—devices that integrate a firewall and VPN with other security features—had been targeted by state-sponsored spies who exploited two zero-day vulnerabilities in the networking giant's gear to compromise government targets globally in a hacking campaign it's calling ArcaneDoor.

The hackers behind the intrusions, which Cisco's security division Talos is calling UAT4356 and which Microsoft researchers who contributed to the investigation have named STORM-1849, couldn't be clearly tied to any previous intrusion incidents the companies had tracked. Based on the group's espionage focus and sophistication, however, Cisco says the hacking appeared to be state-sponsored.

“This actor utilized bespoke tooling that demonstrated a clear focus on espionage and an in-depth knowledge of the devices that they targeted, hallmarks of a sophisticated state-sponsored actor,” a blog post from Cisco's Talos researchers reads.

Cisco declined to say which country it believed to be responsible for the intrusions, but sources familiar with the investigation tell WIRED the campaign appears to be aligned with China's state interests.

Cisco says the hacking campaign began as early as November 2023, with the majority of intrusions taking place between December and early January of this year, when it learned of the first victim. “The investigation that followed identified additional victims, all of which involved government networks globally,” the company's report reads.

In those intrusions, the hackers exploited two newly discovered vulnerabilities in Cisco's ASA products. One, which it's calling Line Dancer, let the hackers run their own malicious code in the memory of the network appliances, allowing them to issue commands to the devices, including the ability to spy on network traffic and steal data. A second vulnerability, which Cisco is calling Line Runner, would allow the hackers' malware to maintain its access to the target devices even when they were rebooted or updated. It's not yet clear if the vulnerabilities served as the initial access points to the victim networks, or how the hackers might have otherwise gained access before exploiting the Cisco appliances.

Cisco has released software updates to patch both vulnerabilities, and advises that customers implement them immediately, along with other recommendations for detecting whether they've been targeted. Despite the hackers' Line Runner persistence mechanism, a separate advisory from the UK's National Cybersecurity Center notes that physically unplugging an ASA device does disrupt the hackers' access. “A hard reboot by pulling the power plug from the Cisco ASA has been confirmed to prevent Line Runner from re-installing itself,” the advisory reads.

The ArcaneDoor hacking campaign represents just the latest series of intrusions to target network perimeter applications sometimes referred to as “edge” devices like email servers, firewalls, and VPNs—often devices intended to provide security—whose vulnerabilities allowed hackers to obtain a staging point inside a victim's network. Cisco's Talos researchers warn of that broader trend in their report, referring to highly sensitive networks that they've seen targeted via edge devices in recent years. “Gaining a foothold on these devices allows an actor to directly pivot into an organization, reroute or modify traffic and monitor network communications,” they write. “In the past two years, we have seen a dramatic and sustained increase in the targeting of these devices in areas such as telecommunications providers and energy sector organizations—critical infrastructure entities that are likely strategic targets of interest for many foreign governments.”

State-sponsored hackers' shift to compromising edge devices has become prevalent enough over the past year that Google-owned security firm Mandiant also highlighted it in its annual M-Trends report earlier this week, based on the company's threat intelligence and incident response findings. The report points to widely exploited vulnerabilities in network edge devices sold by Barracuda and Ivanti and notes that hackers—and specifically espionage-focused Chinese groups—are building custom malware for edge devices, in part because many networks have little or no way to monitor for compromise of the devices. Detecting the ArcaneDoor hackers' access to Cisco ASA appliances, in particular, is “incredibly difficult,” according to the advisory from the UK's NCSC.

Mandiant notes that it has observed Russian state-sponsored hackers targeting edge devices too: It's observed the unit of Russia's GRU military intelligence agency, known as Sandworm, repeatedly hack edge devices used by Ukrainian organizations to gain and maintain access to those victim networks, often for data-destroying cyberattacks. In some cases, the lack of visibility and monitoring in those edge devices has meant that Sandworm was able to wipe a victim network while holding on to its control of an edge device—then hit the same network again.

“They’re systemically targeting security appliances that sit on the edge for access to the rest of the network,” says John Hultquist, Mandiant's head of threat intelligence. “This is no longer an emerging trend. It's established."

Hultquist notes, however, that China is unmatched in its discovery and use of network appliance zero days, like the ones it has used to run rampant through Cisco firewalls over the past several months. He expects more to come, as China's cyberspies continue to turn devices meant to protect target networks against their owners. “It's unlikely these zero days are being produced haphazardly. We suspect a well-resourced, coordinated effort is underway to find and exploit these vulnerabilities,” Hultquist says. “Unfortunately, we'll almost certainly see several more zero-days in security appliances this year.”