The Interlock ransomware operation, launched in late September 2024, is increasingly targeting organizations around the globe. Distinctly, this new threat employs an encryptor specifically designed to attack FreeBSD servers, a relatively uncommon tactic among ransomware groups.
Interlock has already affected six organizations and publicly leaked stolen data after ransoms went unpaid. One prominent victim, Wayne County in Michigan, experienced a cyberattack early in October, adding to the list of affected entities.
Details about Interlock remain limited, with early reports emerging from cybersecurity responder Simo in October. Simo's analysis noted a new backdoor associated with the ransomware, discovered during an investigation on VirusTotal.
Shortly after, MalwareHunterTeam identified a Linux ELF encryptor related to Interlock. Upon further examination, BleepingComputer confirmed that this executable was built specifically for FreeBSD 10.4, though attempts to execute it in a FreeBSD environment failed.
Although ransomware targeting Linux-based VMware ESXi servers is common, an encryptor for FreeBSD is rare. The now-defunct Hive ransomware, disrupted by the FBI in 2023, was the only other known operation with a FreeBSD encryptor.
Trend Micro researchers shared additional samples of the Interlock FreeBSD ELF encryptor and a Windows variant, noting that FreeBSD is often used in critical infrastructure. This likely makes it a strategic target for Interlock, as attacks on these systems can lead to significant service disruptions.
Trend Micro emphasizes that Interlock’s focus on FreeBSD infrastructure allows attackers to disrupt essential services and demand high ransoms, as these systems are integral to many organizations’ operations.
It is important to note that Interlock ransomware is unrelated to any cryptocurrency token of the same name.
While BleepingComputer encountered issues with running the FreeBSD encryptor, they successfully tested the Windows version, which performed actions like clearing event logs and deleting the main binary using rundll32.exe if self-deletion is enabled.
When encrypting files, Interlock appends the .interlock extension and generates a ransom note titled "!README!.txt" in each affected folder. The note explains the encryption, threats, and includes links to a Tor-based negotiation site where victims can communicate with the attackers. Each victim receives a unique ID and email for registration on this negotiation platform.
During attacks, Interlock breaches networks, steals sensitive data, and then deploys the encryptor to lock down files. The data theft supports a double-extortion scheme, with threats to leak data if ransoms—ranging from hundreds of thousands to millions of dollars—are not paid.