Linux Version of Abyss Locker Ransomware Targets VMware ESXi Servers

Cyber Security Threat Summary:
The Abyss Locker operation is the latest to develop a Linux encryptor to target VMware's ESXi virtual machines platform in attacks on the enterprise. As the enterprise shifts from individual servers to virtual machines for better resource management, performance, and disaster recovery, ransomware gangs create encryptors focused on targeting the platform. With VMware ESXi being one of the most popular virtual machine platforms, almost every ransomware gang has begun to release Linux encryptors to encrypt all virtual servers on a device. Other ransomware operations that utilize Linux ransomware encryptors, with most targeting VMware ESXi, include Akira, Royal, Black Basta, LockBit, BlackMatter, AvosLocker, REvil, HelloKitty, RansomEXX, and Hive. Abyss Locker is a relatively new ransomware operation that is believed to have launched in March 2023, when it began to target companies in attacks. Like other ransomware operations, the Abyss Locker threat actors will breach corporate networks, steal data for double-extortion, and encrypt devices on the network. The stolen data is then used as leverage by threatening to leak files if a ransom is not paid. To leak the stolen files, the threat actors created a Tor data leak site named 'Abyss-data' that currently lists fourteen victims. The threat actors claim to have stolen anywhere between 35 GB of data from one company to as high as 700 GB at another.

Security Officer Comments:
The latest variant was uncovered by security researcher MalwareHunterTeam. Taking a closer look at the sample shared, the Linux ELF encryptor utilizes the 'esxcli' command-line VMware ESXi management tool to first list all available virtual machines and then terminate them. Virtual machines are terminated via the ‘vm process kill’ command, further enabling the encryptor to encrypt associated virtual disks, snapshots, and metadata which are then appended with the .vmdk (virtual disks), .vmsd (metadata), and .vmsn (snapshots) extensions. In addition to virtual machines, the ransomware is capable of targeting other files on the victim’s systems which are encrypted and appended with the .crypt extension. Once encryption is successful, a ransom note is left behind which provides instructions on how the victim can recover their data.

Suggested Correction(s):
Backup your data, system images, and configurations, regularly test them, and keep the backups offline: Ensure that backups are regularly tested and that they are not connected to the business network, as many ransomware variants try to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems.

Update and patch systems promptly: This includes maintaining the security of operating systems, applications, and firmware in a timely manner. Consider using a centralized patch management system; use a risk- based assessment strategy to drive your patch management program.

Test your incident response plan: There's nothing that shows the gaps in plans more than testing them. Run through some core questions and use those to build an incident response plan: Are you able to sustain business operations without access to certain systems? For how long? Would you turn off your manufacturing operations if business systems such as billing were offline?

Check Your Security Team's Work: Use a 3rd party pen tester to test the security of your systems and your ability to defend against a sophisticated attack. Many ransomware criminals are aggressive and sophisticated and will find the equivalent of unlocked doors.

Segment your networks: There's been a recent shift in ransomware attacks – from stealing data to disrupting operations. It's critically important that your corporate business functions and manufacturing/production operations are separated and that you carefully filter and limit internet access to operational networks, identify links between these networks and develop workarounds or manual controls to ensure ICS networks can be isolated and continue operating if your corporate network is compromised. Regularly test contingency plans such as manual controls so that safety critical functions can be maintained during a cyber incident.

Train employees: Email remains the most vulnerable attack vector for organizations. Users should be trained how to avoid and spot phishing emails. Multi Factor authentication can help prevent malicious access to sensitive services.