Thousands of Linux Systems Infected by Stealthy Malware Since 2021

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Thousands of Linux systems infected by stealthy malware since 2021:

Thousands of machines running Linux have been infected by a malware strain that's notable for its stealth, the number of misconfigurations it can exploit, and the breadth of malicious activities it can perform, researchers reported Thursday.

The malware has been circulating since at least 2021. It gets installed by exploiting more than 20,000 common misconfigurations, a capability that may make millions of machines connected to the Internet potential targets, researchers from Aqua Security said. It can also exploit CVE-2023-33426, a vulnerability with a severity rating of 10 out of 10 that was patched last year in Apache RocketMQ, a messaging and streaming platform that's found on many Linux machines.

The researchers are calling the malware Perfctl, the name of a malicious component that surreptitiously mines cryptocurrency. The unknown developers of the malware gave the process a name that combines the perf Linux monitoring tool and ctl, an abbreviation commonly used with command line tools. A signature characteristic of Perfctl is its use of process and file names that are identical or similar to those commonly found in Linux environments. The naming convention is one of the many ways the malware attempts to escape notice of infected users.

Perfctl further cloaks itself using a host of other tricks. One is that it installs many of its components as rootkits, a special class of malware that hides its presence from the operating system and administrative tools. Other stealth mechanisms include:

• Stopping activities that are easy to detect when a new user logs in
• Using a Unix socket over TOR for external communications
• Deleting its installation binary after execution and running as a background service thereafter
• Manipulating the Linux process pcap_loop through a technique known as hooking to prevent admin tools from recording the malicious traffic
• Suppressing mesg errors to avoid any visible warnings during execution.

The malware is designed to ensure persistence, meaning the ability to remain on the infected machine after reboots or attempts to delete core components. Two such techniques are (1) modifying the ~/.profile script, which sets up the environment during user login so the malware loads ahead of legitimate workloads expected to run on the server and (2) copying itself from memory to multiple disk locations. The hooking of pcap_loop can also provide persistence by allowing malicious activities to continue even after primary payloads are detected and removed.

Besides running using the machine resources to mine cryptocurrency, Perfctl also turns the machine into a profit-making proxy that paying customers use to relay their Internet traffic. Aqua Security researchers have also observed the malware serving as a backdoor to install other families of malware.

Assaf Morag, Aqua Security's threat intelligence director, wrote in an email:

Perfctl malware stands out as a significant threat due to its design, which enables it to evade detection while maintaining persistence on infected systems. This combination poses a challenge for defenders and indeed the malware has been linked to a growing number of reports and discussions across various forums, highlighting the distress and frustration of users who find themselves infected.

Perfctl uses a rootkit and changes some of the system utilities to hide the activity of the cryptominer and proxy-jacking software. It blends seamlessly into its environment with seemingly legitimate names. Additionally, Perfectl's architecture enables it to perform a range of malicious activities, from data exfiltration to the deployment of additional payloads. Its versatility means that it can be leveraged for various malicious purposes, making it particularly dangerous for organizations and individuals alike.

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