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Newly Discovered 'Turla' Malware Targets Linux Systems

Researchers at Kaspersky Lab have uncovered a new malware sample designed to target Linux operating systems. The malware has been used by the notorious advanced persistent threat (APT) group called "Turla" (also known as Snake and Uroburos).

The Turla cyber espionage toolkit has been in development for almost ten years, being utilized in numerous operations aimed at organizations across the world. One of the more recent campaigns, dubbed Epic Turla, targeted government organizations, intelligence agencies, educational institutions, embassies, military groups, and research and pharmaceutical companies in over 45 countries.

Up until recently, researchers had only seen Turla components designed to target Windows operating systems in the wild. However, on Monday, Kaspersky Lab reported uncovering two samples that target Linux.

Researchers believe one of the samples, detected as HEUR:Backdoor.Linux.Turla.gen, might have been active for years on a target's website, but currently, there is no sufficient evidence to back up this theory.

"The Linux Turla module is a C/C++ executable statically linked against multiple libraries, greatly increasing its file size. It was stripped of symbol information, more likely intended to increase analysis effort than to decrease file size. Its functionality includes hidden network communications, arbitrary remote command execution, and remote management. Much of its code is based on public sources," Kaspersky's Kurt Baumgartner and Costin Raiu explained in a blog post.

The Linux Turla component is based on "cd00r," a proof-of-concept backdoor that's designed to provide remote access to a system without showing an open port all the time, which makes it stealthier than standard backdoors.

"This Turla cd00r-based malware maintains stealth without requiring elevated privileges while running arbitrary remote commands. It can't be discovered via netstat, a commonly used administrative tool. It uses techniques that don't require root access, which allows it to be more freely run on more victim hosts. Even if a regular user with limited privileges launches it, it can continue to intercept incoming packets and run incoming commands on the system," researchers noted.

The command and control (C&C) mechanism leverages TCP/UDP packets, and one of the hardcoded C&C domains used by the malware has been previously linked to Turla operations. The said C&C domain has been sinkholed by Kaspersky.

Another Linux Turla sample, discovered by the security firm on Monday, is believed to be part of a different generation. The threat was detected by Kaspersky's products due to similarities with the other Linux Turla module.

Earlier this year, researchers detailed the connection between Turla and Agent.BTZ, the piece of malware that became notorious in 2008 after it was used in a cyberattack targeting the networks of the United States military.

Last month, G Data published a report on a new remote access Trojan, ComRAT, that appears to be a successor of Agent.BTZ. Researchers have pointed out that the existence and sophistication of ComRAT demonstrate that the Turla campaign is still active.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.