Cybercriminals behind the AvosLocker ransomware attack employed a tactic of infecting organizations through Open-Source Remote Administration Tools.
This method allowed the malware to spread rapidly, potentially compromising sensitive data and systems across the affected networks.
The FBI found a new version of AvosLocker in May of 2023 during their investigations.
AvosLocker is a RaaS (ransomware as a service) group that emerged in the middle of 2021. It has since gained notoriety for attacks on U.S. financial institutions, vital factories, and government buildings, all considered part of the country’s “critical infrastructure.”
Members of the AvosLocker group infiltrate corporate networks by masquerading as genuine software installers or by employing freely available remote system administration tools.
Affiliates of AvosLocker engage in extortion by threatening to leak or publicly disclose the stolen information obtained through data exfiltration.
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- Remote system administration tools—Splashtop Streamer, Tactical RMM, PuTTy, AnyDesk, PDQ Deploy, and Atera Agent—as backdoor access vectors [T1133].
- Scripts to execute legitimate native Windows tools [T1047], such as PsExec and Nltest.
- Open-source networking tunneling tools [T1572] Ligolo and Chisel.
- Cobalt Strike and Sliver for command and control (C2).
- Lazagne and Mimikatz for harvesting credentials [T1555].
- FileZilla and Rclone for data exfiltration.
- Notepad++, RDP Scanner, and 7zip
The FBI developed the following YARA rule to detect the signature of a file known to be enabling malware, based on an analysis by a sophisticated digital forensics group.
NetMonitor.exe is a malware masquerading as a legitimate process and it has the appearance of a genuine network monitoring tool.
The network will get a ping from this persistence utility every five minutes.
The software for NetMonitor is set up to talk to a specific IP address that acts as its command server through TCP port 443.
During an attack, the communication between NetMonitor and the command server is protected, and NetMonitor works like a reverse facilitator that lets attackers connect to the tool from outside the victim’s network.
The FBI and CISA suggest that companies take steps to protect their computer systems from AvosLocker ransomware attacks. This will help to prevent hackers from stealing important information and causing problems.