Volt Typhoon, a China-government backed hacking group that has infiltrated America’s critical infrastructure networks for years, has consistently built and dismantled ephemeral malicious infrastructure to burrow into hundreds of sensitive systems undetected, Lumen Technologies’ Black Lotus Labs said in a Wednesday report.
The covert access operation that researchers call “Silent Train” isn’t a standalone network, but rather a series of compromised small office home office (SOHO) routers, internet of things (IoT) devices and enterprise infrastructure that Volt Typhoon has rapidly rotated through since late 2023.
The Chinese threat group has used this chain of short-lived compromised infrastructure to exploit additional vulnerabilities, including zero-days, in network edge devices and gain deeper, persistent access into victim networks, researchers said.
“Individual chains are assembled and dismantled every day, with infrastructure continually refreshed,” Michael Horka, principal information security engineer at Black Lotus Labs, told CyberScoop. “Volt Typhoon demonstrated a repeatable capability to rebuild a new chain with different infrastructure in less than two minutes, making the number of nodes at any one moment effectively close to zero.”
Black Lotus Labs has notified hundreds of victims since it first identified Silent Train activity, including telecom providers, government entities, defense contractors, communication services, universities and IT firms. Other victims spanning critical infrastructure include organizations in the water, energy, transportation, maritime, rail, aviation and emergency services sectors.
“The ephemeral nature of the framework means our observations should not be interpreted as a complete census of Volt Typhoon activity,” said Horka, who also was the lead researcher on the report.
The nation-state group’s investment in operational security and preserving access is remarkable, according to Black Lotus Labs.
“We observed infrastructure assembled in under two minutes, sessions averaging roughly four hours, extensive cleanup, compartmentalization and continued development of new access vectors,” Horka said. “That is considerable effort devoted not even to get into their end targets, but purely to making important operations difficult to discover and trace.”
Volt Typhoon relied more heavily on Silent Train after the FBI and Justice Department disrupted the KV Botnet in early 2024, researchers said. Earlier this year, U.S. and global authorities warned about a widespread shift in Chinese hacking groups’ use of covert networks riding on compromised common devices.
The reach of those efforts is extensive and ongoing. Volt Typhoon has exploited and abused more than 27 device classes in Silent Train operations, including edge devices, enterprise management tools, identity and access management systems, networking infrastructure and other technologies.
“The diversity matters, but the discipline matters even more,” Horka said. “Specific device types were consistently reserved for particular positions in the chain. It operated less like a collection of randomly compromised devices and more like an organized inventory of capabilities.”
The threat group has successfully compromised devices and technologies from Fortinet, Cisco, ManageEngine, Ivanti, F5, Check Point, Palo Alto Networks, ServiceNow, TP-Link, Netgear and ArcGIS, researchers said. Black Lotus Labs also observed confirmed zero-day campaigns targeting Versa Director, N-Able N-Central, Cisco Catalyst SD-WAN and VeloCloud Orchestrator.
“The exploitation patterns, victimology, and geographic targeting observed throughout our investigation point to a sustained focus on communications, defense, government, and critical infrastructure environments of enduring strategic value,” Black Lotus Labs researchers wrote in the report. “Through repeated targeting of centralized management platforms and control-plane technologies, Silent Train shows how Volt Typhoon systematically pursues and preserves access to some of the most consequential networks in the United States.”
Silent Train’s ephemerality and operational discipline means it can’t be measured in size. These attributes also make it “fundamentally difficult to disrupt because there isn’t one network to take down,” Horka said.
“What exists today will be completely different tomorrow,” he added. “You can try to remove individual pieces, but removing the actor’s ability to continuously rebuild them is a much harder problem to solve.”
