FontOnLake: "Sophisticated" malware targets Linux systems
The malware stands out for its ability to maintain persistence on the infected system
Present since at least May 2020, according to samples uploaded to VirusTotal, the malware stands out for its ability to maintain persistence on the infected system and for the sophistication of its design.
Its installation is done through modified and trojanized versions of popular Linux commands, normally present in the coreutils package or installed by default on some systems. These commands include cat, kill, sftp, and sshd, and often launch at system startup and allow the malware to be persistent. They are also used to install custom backdoors and rootkits.
Researchers have discovered three custom backdoors written in C ++, which are related to FontOnLake malware and provide operators with remote access to the infected system.
“All the trojanized files are standard Linux utilities and each serves as a persistence method because they are commonly executed on system start-up. The initial way in which these trojanized applications get to their victims is not known,” said Vladislav Hrčka, malware analyst and reverse engineer at ESET.
Once the malware is on the system, it uses the installed backdoors to retrieve credentials and Bash history, and then sends them to its command and control (C&C) server. The rootkits in turn are used to allow malware to hide its existence and activities on the system of the victim.
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The communication between trojanized apps and rootkit is done through a virtual file created by the latter. An operator can read or write data to this file and extract it from the backdoor component.
Researchers suspect that FontOnLake is being used for targeted attacks. Its creators are also careful: different C&C servers are used in each of the samples on VirusTotal and have since been deactivated. Analysis seems to indicate that the virus is present in Southeast Asia. Some of the samples show that Debian and CentOS are among the targeted distributions.
“Companies or individuals who want to protect their Linux endpoints or servers from this threat should use a multilayered security product and an updated version of their Linux distribution,” said Hrčka.
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