Interlock ransomware is a relatively new but increasingly prominent ransomware threat actor first observed in September 2024 and gaining significant activity in 2025. Unlike typical Ransomware-as-a-Service (RaaS) models that rely on affiliates and public recruitment, Interlock operates as a closed, self-contained group without affiliates or public advertisements, indicating a potentially more controlled and sophisticated operation. Their attack methodology involves double extortion campaigns, where data is not only encrypted but also exfiltrated to pressure victims into paying ransoms to avoid public data leaks. The initial access vector is primarily through social engineering, specifically fake software updaters that trick users into executing malicious payloads. Once inside a network, the group leverages PowerShell scripts for execution and persistence, and deploys custom remote access trojans (RATs) such as Interlock RAT, NodeSnake RAT, and SystemBC, which facilitate lateral movement, reconnaissance, and command and control (C2) communications. The use of tools like Cobalt Strike (noted as s0154) suggests advanced post-exploitation capabilities. The group targets a broad range of sectors including education, healthcare, technology, and government entities across North America and Europe, with notable incidents such as the DaVita breach and the ransomware attack on St. Paul, Minnesota. The tactics, techniques, and procedures (TTPs) employed align with MITRE ATT&CK techniques including scheduled task execution (T1053.005), PowerShell execution (T1059.001), system information discovery (T1082), and defense evasion (T1562.001). The absence of known exploits in the wild suggests that the group relies heavily on social engineering and custom malware rather than exploiting public vulnerabilities. Overall, Interlock represents a medium-severity ransomware threat with sophisticated social engineering and multi-stage attack chains that can cause significant operational disruption and data compromise.

For European organizations, the Interlock ransomware threat poses a substantial risk to confidentiality, integrity, and availability of critical systems and data. The double extortion approach means that even if organizations have robust backups and can restore encrypted data, they remain vulnerable to data leaks that can damage reputation and lead to regulatory penalties under GDPR. Sectors such as healthcare and government are particularly sensitive due to the critical nature of their services and the potential impact on public safety and trust. The use of social engineering and fake software updaters increases the likelihood of successful initial compromise, especially in environments with less mature user awareness programs. The deployment of custom RATs and Cobalt Strike frameworks enables attackers to maintain persistence, escalate privileges, and move laterally, potentially compromising large parts of an organization's network before detection. This can lead to prolonged downtime, loss of sensitive data, and significant financial costs related to incident response, remediation, and potential ransom payments. Additionally, the targeting of education and technology sectors could disrupt research, intellectual property, and innovation activities within Europe. Given the geopolitical climate and the strategic importance of these sectors, European organizations must consider Interlock a credible and evolving threat.

To mitigate the threat posed by Interlock ransomware, European organizations should implement a multi-layered defense strategy tailored to the group's TTPs. First, enhance user awareness training focusing on recognizing social engineering attempts, particularly fake software update prompts and unsolicited download links. Deploy application control and endpoint detection and response (EDR) solutions capable of detecting PowerShell abuse and anomalous script execution. Restrict the use of PowerShell and other scripting environments to only trusted administrators and monitor their usage closely. Implement network segmentation to limit lateral movement opportunities for attackers deploying RATs and Cobalt Strike beacons. Employ robust email filtering and web gateway solutions to block access to compromised websites used for payload delivery. Regularly audit and harden scheduled tasks and persistence mechanisms to detect unauthorized modifications. Maintain offline, immutable backups and test restoration procedures frequently to ensure resilience against encryption. Additionally, deploy threat hunting and anomaly detection to identify early signs of compromise, such as unusual network traffic patterns or new service creations. Finally, establish incident response plans that include procedures for double extortion scenarios, including legal and communication strategies to handle potential data leaks.