The Interlock ransomware group has been actively targeting businesses and critical infrastructure sectors across North America and Europe since September 2024. This ransomware employs strong cryptographic techniques, specifically AES-256-GCM for symmetric encryption of files combined with RSA-4096 for key protection, leveraging the OpenSSL library to efficiently perform encryption operations. The malware is designed with code obfuscation to evade detection and analysis, and it accepts specific command-line arguments to modify its behavior during execution. Notably, it excludes certain folders, file extensions, and files from encryption to avoid system instability or damage, which is a tactic often used to maintain system operability and increase the likelihood of ransom payment. During the encryption process, Interlock ransomware changes the file extensions to '.!NT3RLOCK' and may forcibly terminate processes to unlock files for encryption. Beyond encrypting data, the group exfiltrates sensitive information and threatens public disclosure to coerce victims into paying ransom, a double extortion tactic that increases pressure on targeted organizations. Communication and ransom negotiations are conducted via a Tor-based hidden service, enhancing the attackers' anonymity. The group also references legal regulations in their communications to intimidate victims and justify their demands. While no known exploits in the wild have been reported for initial infection vectors, the ransomware’s operational sophistication and targeting of critical infrastructure highlight its threat level. The recommended defensive measures include maintaining offsite backups and conducting regular recovery drills to ensure rapid restoration of systems in case of infection.

For European organizations, the Interlock ransomware poses significant risks to confidentiality, integrity, and availability of critical business data and operational systems. The use of strong encryption algorithms and key protection mechanisms means that without backups or decryption keys, data recovery is virtually impossible. The double extortion tactic—data theft combined with encryption—exposes organizations to reputational damage, regulatory penalties under GDPR for data breaches, and potential operational disruptions. Critical infrastructure sectors, such as energy, healthcare, and transportation, are particularly vulnerable due to their essential services and potential cascading effects on public safety and economic stability. The threat of public data disclosure increases the risk of intellectual property loss and customer trust erosion. The ransomware’s ability to terminate processes can disrupt ongoing operations and cause downtime. European organizations may also face legal and compliance challenges, as attackers reference legal regulations to pressure victims, complicating incident response and ransom negotiation strategies.

Beyond standard recommendations, European organizations should implement the following specific measures: 1) Conduct thorough network segmentation to limit ransomware lateral movement, especially isolating critical infrastructure systems. 2) Deploy advanced endpoint detection and response (EDR) solutions capable of detecting code obfuscation and process termination attempts characteristic of Interlock ransomware. 3) Regularly audit and restrict administrative privileges to reduce the risk of privilege escalation and ransomware deployment. 4) Implement strict application whitelisting to prevent execution of unauthorized binaries, including those with known hashes associated with Interlock. 5) Monitor network traffic for connections to Tor networks or unusual outbound encrypted traffic indicative of ransomware communication. 6) Maintain immutable, offline backups with frequent recovery testing to ensure data integrity and availability. 7) Develop and rehearse incident response plans that include legal and regulatory considerations, given the attackers’ use of legal references in negotiations. 8) Educate employees on phishing and social engineering tactics, as initial infection vectors often exploit human factors. 9) Collaborate with national cybersecurity agencies and share threat intelligence to stay updated on emerging tactics and indicators of compromise related to Interlock.