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Evilnum Cyberspies Update Arsenal in Recent Attacks

The threat group tracked as Evilnum was observed using updated tactics and tools in recent attacks, Cybereason’s Nocturnus research team reported last week.

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.

Focused on espionage, Evilnum recently switched from delivering ZIP archives containing multiple LNK files (via spear-phishing) to including a single LNK in the archive, which masquerades as a PDF, Cybereason reveals. Once executed, the shortcut writes to disk a JavaScript that replaces the LNK with the actual PDF.

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.

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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.

“In recent weeks we observed a significant change in the infection procedure of the group, moving away from the JavaScript backdoor capabilities, instead utilizing it as a first stage dropper for new tools down the line. During the infection stage, Evilnum utilized modified versions of legitimate executables in an attempt to stay stealthy and remain undetected by security tools. […] This innovation in tactics and tools is what allowed the group to stay under the radar, and we expect to see more in the future as the Evilnum group’s arsenal continues to grow,” the Nocturnus researchers conclude.

Related: Hack-for-Hire Group Targets Financial Sector Since 2012

Related: Evilnum Group Targets Fintech Companies in Europe

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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