Security researchers with Kaspersky have analyzed a UEFI firmware rootkit that appears to target specific motherboard models from Gigabyte and Asus.
Dubbed CosmicStrand and likely developed by an unknown Chinese-speaking threat actor, the rootkit was found located in the firmware images of Gigabyte and Asus motherboards using the H81 chipset, suggesting that a common vulnerability may have been exploited for infection.
Kaspersky believes that the firmware changes might have been performed with an automated patcher, which would imply that the attacker either had physical access to the infected motherboards or used an implant already running on the motherboards.
The infected firmware images contain a ‘CSMCORE DXE’ driver – which facilitates the system boot in legacy mode via the MBR – that had been patched with code that runs at system startup to trigger an execution chain leading to the deployment of a kernel-level implant in Windows.
A malicious hook set up in the boot manager allows the threat to modify the Windows kernel loader before it runs, to set up a second hook called at a later stage of the start-up process, to take control over the execution process and inject a shellcode in memory. Next, after a sleep period, the malware fetches the final payload.
CosmicStrand was also seen attempting to disable the PatchGuard security mechanism.
A user-mode sample Kaspersky’s researchers found in the memory of an infected machine – and which is likely linked with CosmicStrand – was designed to run command lines to create a user account added to the local administrators group.
The researchers identified two variants of the rootkit, one used between the end of 2016 and mid-2017, and another active in 2020, each of them with its own command and control (C&C) server.
The CosmicStrand victims identified by Kaspersky are private individuals from China, Iran, Russia, and Vietnam, none of them related to a specific organization or industry.
Chinese cybersecurity company Qihoo 360 analyzed an earlier version of the malware back in 2017 after it had been contacted by an individual who had trouble removing a highly persistent piece of malware. The firm, which named the malware ‘Spy Shadow Trojan’, reported that the victim had acquired the infected motherboard, which had been previously owned by someone else, from an online store.
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