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ESET: FontOnLake Rootkit Malware Targets Linux Systems

 

Researchers have detected a new campaign that is potentially targeting businesses in Southeast Asia using previously unknown Linux malware that is designed to allow remote access to its administrators, as well as collect credentials and operate as a proxy server. 

The malware group, called "FontOnLake" by the Slovak cybersecurity firm ESET, is reported to entail "well-designed modules" that are constantly modified with a wide range of features, indicating an active development stage. 

According to samples uploaded to VirusTotal, the initial attacks employing this threat may have happened as early as May 2020. The same virus is being tracked by Avast and Lacework Labs under the name HCRootkit. 

ESET researcher Vladislav Hrčka stated, "The sneaky nature of FontOnLake's tools in combination with advanced design and low prevalence suggest that they are used in targeted attacks." 

"To collect data or conduct other malicious activity, this malware family uses modified legitimate binaries that are adjusted to load further components. In fact, to conceal its existence, FontOnLake's presence is always accompanied by a rootkit. These binaries are commonly used on Linux systems and can additionally serve as a persistence mechanism." 

FontOnLake's toolkit consists of three components: trojanized copies of genuine Linux utilities utilized to load kernel-mode rootkits and user-mode backdoors, all of which interact through virtual files. The C++-based implants themselves are programmed to monitor systems, discreetly perform commands on networks, and steal account passwords. 

A second variation of the backdoor also function as a proxy, modify files, and download arbitrary files, while a third variant, in addition to combining characteristics from the other two backdoors, can run Python scripts and shell commands. 

ESET discovered two variants of the Linux rootkit that are based on an open-source project called Suterusu and share features like hiding processes, files, network connections, and itself, as well as being able to perform file operations and obtain and run the user-mode backdoor. 

Enterprise Password Management 

It is yet unknown how the attackers gained initial network access but the cybersecurity firm highlighted that the malicious actor behind the assaults is "overly cautious" to avoid leaving any traces by depending on multiple, unique command-and-control (C2) servers with different non-standard ports. All the C2 servers observed in the VirusTotal artifacts are no longer working. 

Hrčka stated, "Their scale and advanced design suggest that the authors are well versed in cybersecurity and that these tools might be reused in future campaigns." 

"As most of the features are designed just to hide its presence, relay communication, and provide backdoor access, we believe that these tools are used mostly to maintain an infrastructure which serves some other, unknown, malicious purposes."