Interlock Ransomware: A Deep Dive into a Novel Threat Landscape

Interlock Ransomware: A Deep Dive into a Novel Threat Landscape

A new ransomware variant, Interlock, has emerged, targeting businesses and critical infrastructure in North America and Europe since September 2024. This presents a significant cybersecurity challenge due to its unique infection methods, double extortion model, and cross-platform capabilities. Understanding Interlock’s tactics, techniques, and procedures (TTPs) is crucial for organizations to bolster their defenses and mitigate the risk of costly disruptions. The advisory, released jointly by the FBI, CISA, HHS, and MS-ISAC, highlights the urgency of proactive security measures and provides specific recommendations for improved cyber resilience.

Background

Interlock ransomware, first observed in late September 2024, displays opportunistic, financially motivated behavior. Its actors deploy encryptors compatible with both Windows and Linux systems, notably targeting virtual machines (VMs) across both operating systems. Unlike many ransomware groups, Interlock actors have demonstrated use of drive-by downloads from compromised legitimate websites for initial access, a less common but highly effective tactic. They also utilize the “ClickFix” social engineering technique, deceiving victims into executing malicious payloads disguised as CAPTCHA fixes or software updates. Once inside, the actors employ various methods for reconnaissance, credential access, and lateral movement before encrypting data and exfiltrating it as part of a double extortion scheme.

Deep Analysis

Interlock’s success stems from a combination of factors. The drive-by download method leverages the trust users place in legitimate websites, bypassing traditional security measures. The ClickFix technique exploits human error, relying on the user’s lack of awareness and tendency to trust prompts from familiar-looking interfaces. The double extortion model—simultaneous encryption and data exfiltration—significantly increases pressure on victims to pay, as they face both data loss and public exposure. The use of both Windows and Linux encryptors expands the potential target base significantly, impacting a wider range of organizations. The deployment of tools like Cobalt Strike, SystemBC, and custom-built RATs (Remote Access Trojans) such as NodeSnake shows a high level of technical sophistication and adaptability.

The observed use of Azure Storage Explorer and AzCopy for data exfiltration indicates the actors’ familiarity with cloud technologies and their ability to leverage readily available tools to facilitate the process. While the advisory notes similarities between Interlock and the Rhysida ransomware, the exact nature of this relationship remains unconfirmed in the provided text. The lack of an initial ransom demand, instead providing a unique code for contact via a Tor .onion URL, is an intriguing aspect, suggesting a focus on personalized negotiation and potentially a higher likelihood of successful extortion attempts.

Pros

• Comprehensive Advisory: The joint advisory provides a detailed and well-structured overview of Interlock’s TTPs, including Indicators of Compromise (IOCs), enabling organizations to proactively improve their security postures.
• Actionable Mitigations: The advisory offers concrete and practical mitigation strategies aligned with CISA’s Cybersecurity Performance Goals (CPGs), allowing organizations to take immediate steps to reduce their vulnerability.
• Cross-Sector Collaboration: The collaboration between FBI, CISA, HHS, and MS-ISAC demonstrates a coordinated effort to combat this threat, maximizing resources and disseminating information effectively across different sectors.

Cons

• Evolving Tactics: The advisory highlights the adaptability of Interlock actors, and their techniques are likely to evolve further, requiring continuous monitoring and updates to security measures.
• Drive-by Download Vulnerability: Drive-by downloads remain a significant challenge, relying on compromised websites beyond the control of individual organizations. A broader industry-wide effort to secure website infrastructure is necessary.
• Social Engineering Reliance: Success of the ClickFix technique relies on human error and highlights the ongoing need for effective cybersecurity awareness training programs for all employees.

What’s Next

The near-term implications involve a heightened focus on proactive security measures. Organizations should prioritize implementing the recommended mitigations, especially regarding network segmentation, robust endpoint detection and response (EDR) solutions, and enhanced security awareness training. Continuous monitoring for suspicious activity and timely patching of vulnerabilities are critical. Closely monitoring the development of Interlock, particularly potential variations in TTPs, and sharing information with relevant security agencies, will be vital in responding to and mitigating future attacks. The continued exploration and analysis of the relationship between Interlock and Rhysida will provide further insight into the broader threat landscape.

Takeaway

Interlock ransomware presents a serious threat due to its novel infection techniques and the effectiveness of its double extortion model. While the joint advisory provides valuable insights and actionable steps for mitigation, organizations must proactively implement robust security practices, prioritize employee training, and maintain vigilance against evolving attack methods. A layered defense approach combining technical solutions and employee awareness is crucial for combating this and similar threats.

Source: CISA Cybersecurity Advisories