The threat group tracked as Evilnum was observed using updated tactics and tools in recent attacks, Cybereason’s Nocturnus research team reported last week.
Initially detailed in 2018, Evilnum appears to have been active for nearly a decade, offering ‘mercenary’ hack-for-hire services, a recent report from Kaspersky revealed.
Furthermore, the hackers have adopted a scheduled task to ensure persistence, moving away from the previously used Run registry key. The scheduled task retrieves and executes the next stage payload, a modified version of “Java Web Start Launcher.”
This payload, however, was designed as a downloader for the next stage, another downloader that instead fetches the final payload and runs it directly in memory, with a scheduled task named “Adobe Update Task.”
Dubbed PyVil RAT and written in Python, the delivered malware was designed to log keystrokes, run cmd commands, take screenshots, download additional Python scripts to expand functionality, drop and upload executables, open an SSH shell, and collect system information (running antivirus program, connected USB devices, Chrome version).
The malware communicates with its command and control (C&C) server via HTTP POST requests that are RC4-encrypted.
Cybereason’s security researchers also observed PyVil RAT receiving from the C&C a custom version of the LaZagne Project, which was employed by the group before. The script was meant to dump passwords and collect cookie information.
The researchers also noticed a change in the attackers’ infrastructure: while in previous attacks the hackers only used IP addresses in C&C communications, over the past several weeks they switched to employing domains for the same operations, and appear to be changing domains at a rapid pace.
Evilnum has remained constant in the targeting of European fintech companies over the past couple of years, but evolved tactics, techniques and procedures (TTPs) to ensure the success of its attacks, and the recent changes are not surprising.