A strain of malware has been exploiting misconfigurations on Linux servers since 2021 and has been found to be quite challenging to remove. The malware has been dubbed perfctl and, as you might expect, mines cryptocurrency.

The developers of this malware are as of yet unknown and have created a malicious piece of software that uses processes and file names that are either identical or very similar to those already found in Linux environments.

To keep itself hidden, perfctl uses several tricks, one of which is to install many of its components as rootkits, which are harder to detect by nature. Perfctrl also stops all easily detected activities when a user logs in, uses a Unix socket over Tor for communication, deletes the installation binary after the service is up and running, manipulates the pcap_loop process by way of hooking to obfuscate the malware, and suppresses error messages to avoid warnings during execution.

In regards to perfctl, Assaf Morag, a researcher for Aqua Security, said, "The main impact of the attack is resource hijacking. In all cases, we observed a monero cryptominer (XMRIG) executed and exhausting the server’s CPU resources. The cryptominer is also packed and encrypted. Once unpacked and decrypted it communicates with cryptomining pools." Morag continues, "To detect Perfctl malware you look for unusual spikes in CPU usage, or system slowdown if the rootkit has been deployed on your server. These may indicate cryptomining activities, especially during idle times."

To mitigate against perfctl, you should make sure all Linux servers are patched for all known vulnerabilities, set noexec on /tmp and /dev/shm, disable unused services, implement strict privilege management, isolate critical servers from the Internet or use firewalls to restrict outbound communication, and deploy runtime protection.