China-linked APT Bronze Starlight deploys ransomware as a smokescreen

China-linked APT Bronze Starlight is deploying post-intrusion ransomware families as a diversionary action to its cyber espionage operations.

Researchers from Secureworks reported that a China-linked APT group, tracked as Bronze Starlight (APT10), is deploying post-intrusion ransomware families to cover up the cyber espionage operations.

The experts observed an activity cluster involving post-intrusion ransomware such as LockFile, Atom Silo, Rook, Night Sky, Pandora, and LockBit 2.0.

However, the victimology, the short lifespan of each ransomware family employed in the attacks, and access to malware used by nation-state actors suggest that the main motivation of the group may be intellectual property theft or cyberespionage. The victims include pharmaceutical companies in Brazil and the U.S., a U.S.-based media organization with offices in China and Hong Kong, electronic component designers and manufacturers in Lithuania and Japan, a law firm in the U.S., and an aerospace and defense division of an Indian conglomerate.

“The ransomware could distract incident responders from identifying the threat actors’ true intent and reduce the likelihood of attributing the malicious activity to a government-sponsored Chinese threat group.” reads the report published by the experts. “The operational cadence and victimology of LockFile, AtomSilo, Rook, Night Sky, and Pandora deployments do not align with conventional financially motivated cybercrime operations. In each case, the ransomware targets a small number of victims over a relatively brief period of time before it ceases operations, apparently permanently.”

Bronze Starlight, active since mid-2021, is also tracked by Microsoft under the emerging threat cluster moniker DEV-0401, with the tech giant emphasizing its involvement in all stages of the ransomware attack cycle right from initial access to the payload deployment.

A group’s hallmark is the use of the HUI Loader, which is a custom DLL loader loaded by legitimate programs that are vulnerable to DLL search order hijacking. The HUI Loader is used to decrypt and load a third file containing an encrypted payload that is also deployed to the infected host.

Since early 2021, Secureworks CTU researchers observed threat actors deploying HUI Loader in a campaign aimed at intellectual property theft and primarily targeting Japanese organizations. The HUI Loader was employed to load the SodaMaster RAT. The experts pointed out that the victimology and tactics, techniques, and procedures in this campaign align with BRONZE RIVERSIDE activity.

In mid-2021, CTU researchers began tracking a second cluster of activity that uses HUI Loader to load Cobalt Strike Beacon and deploy ransomware. CTU researchers attribute this second cluster of activity to the BRONZE STARLIGHT threat group.

Experts noticed that the HUI Loader samples used to load Cobalt Strike Beacon were involved in the deployment of LockFile, AtomSilo, Rook, Night Sky, and Pandora ransomware.

“The use of HUI Loader to load Cobalt Strike Beacon, the Cobalt Strike Beacon configuration information, the C2 infrastructure, and the code overlap suggest that the same threat group is associated with these five ransomware families. It is likely that BRONZE STARLIGHT is responsible for LockFile, AtomSilo, Rook, Night Sky, and Pandora intrusion activity.” continues the analysis.

CTU pointed out that four HUI Loader samples decrypt and load PlugX RAT payloads, a malware historically used by multiple Chinese threat groups.

“BRONZE STARLIGHT compromises networks by exploiting vulnerabilities in network perimeter devices, including known vulnerabilities for which patches are available. The threat actors deploy HUI Loader to decrypt and execute a Cobalt Strike Beacon for command and control. They then deploy ransomware and exfiltrate sensitive data from the victim’s environment.” concludes the report. “Both the exploitation of known vulnerabilities and the use of the Cobalt Strike for command and control provide opportunities to detect and prevent BRONZE STARLIGHT intrusion activity before exfiltration or ransomware deployment.” 

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Pierluigi Paganini

(SecurityAffairs – hacking, Bronze Starlight)