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Turla's Updated ComRAT Malware Uses Gmail for C&C Communication

An updated version of the ComRAT malware that Russia-linked cyber-espionage threat actor Turla has been using in recent attacks can connect to Gmail to receive commands, ESET reports.

Also referred to as Snake, Venomous Bear, KRYPTON, and Waterbug, the hacking group is believed to have been active since at least 2006, based on the use of ComRAT, also known as Agent.BTZ and Chinch.

One of the oldest malware families used by the group, ComRAT was used to target the US military in 2008 and saw two major versions released until 2012, both derived from the same code base. By 2017, the hackers had made few changes to the malware.

ComRAT v4, the iteration released in 2017, is far more complex compared to its predecessors, and is known to have been in use even in attacks employed this year, ESET’s security researchers report. The first sample of ComRAT v4 appears to have been compiled in April 2017, while the most recent one is dated November 2019.

To date, Turla has used the malware to target at least three victims (two Ministries of Foreign Affairs and a national parliament) for the exfiltration of sensitive documents to public cloud services such as OneDrive and 4shared.

Developed in C++, ComRAT v4 is deployed through existing access methods, such as the PowerStallion PowerShell backdoor, and has two command and control (C&C) channels, namely HTTP (the same protocol employed in the previous variant) and email (can receive commands and exfiltrate data via Gmail).

Relying on cookies stored in the configuration file, the malware can connect to the Gmail web interface to check an inbox and download attachments containing encrypted commands that the attackers have sent from a different address.

The new malware variant is named Chinch internally (the same as previous versions), shares part of its network infrastructure with Mosquito, and has been observed being dropped or dropping Turla malware such as a customized PowerShell loader, the PowerStallion backdoor, and the RPC backdoor.

Mainly designed for the exfiltration of confidential documents, ComRAT v4 also allows attackers to deploy additional malware onto the compromised environments. Furthermore, operators can run commands to gather information from the compromised systems, such as Active Directory groups or users, network details, and Microsoft Windows configurations.

The malware’s components include an orchestrator, injected into explorer.exe, which controls most functions, a communication module (DLL) injected into the default browser by the orchestrator, and a Virtual FAT16 File System containing configuration and logs.

The security researchers also observed a focus on evasion, with the hackers regularly exfiltrating security-related log files to assess whether their tools have been detected or not.

“Its most interesting feature is the use of the Gmail web UI to receive commands and exfiltrate data. Thus, it is able to bypass some security controls because it doesn’t rely on any malicious domain. We also noticed that this new version abandoned the use of COM object hijacking for persistence, the method that gave the malware its common name,” the researchers note.

With ComRAT v4 still in use at the beginning of this year, it’s clear that Turla continues to be an active threat to diplomats and militaries, ESET concludes.

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