Cisco Firewall Exploited in Interlock Ransomware Attacks: Zero-Day Vulnerability

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Cisco Secure Firewall Management Center Vulnerability Exploited by Interlock Group

A recently patched vulnerability in Cisco’s Secure Firewall Management Center (FMC) software has been exploited by the Interlock cybercrime group as a zero-day since late January.

Vulnerability Details

The vulnerability, tracked as CVE-2026-20131, affects the web-based management interface of FMC software and can be exploited by a remote, unauthenticated attacker to execute arbitrary Java code with root privileges.

According to Amazon’s threat intelligence team, the Interlock group has been using the vulnerability to launch ransomware attacks against various sectors, including education, engineering, architecture, construction, manufacturing, healthcare, and government entities.

Threat Actor’s Tactics and Infrastructure

The group’s tactics, techniques, and procedures (TTPs) involve exploiting the vulnerability to gain initial access to the targeted network, followed by the deployment of custom remote access trojans (RATs), reconnaissance scripts, and evasion techniques.

An analysis of the threat actor’s infrastructure and activity patterns suggests that they likely operate in the UTC+3 time zone, with peak activity between 12:00 and 18:00 and a low-activity window from approximately 00:30 to 08:30.

Indicators of Compromise and Mitigation

Amazon has shared indicators of compromise (IoCs) to help defenders detect and block Interlock ransomware attacks.

The IoCs include domains, IP addresses, and other technical details that can be used to identify and mitigate the threat.

Importance of Prompt Patching and Vulnerability Management

The exploitation of the CVE-2026-20131 vulnerability highlights the importance of prompt patching and vulnerability management.

Cisco had announced the availability of patches for the vulnerability on March 4, and customers are advised to apply the patches as soon as possible to prevent exploitation.

Robust Threat Detection and Response Capabilities

The Interlock group’s use of the zero-day vulnerability also underscores the need for organizations to have robust threat detection and response capabilities in place.

This includes implementing advanced threat detection tools, conducting regular security audits, and providing ongoing training and awareness programs for security personnel.

Human Element of Cybersecurity

In addition to the technical measures, organizations should also consider the human element of cybersecurity.

The Interlock group’s TTPs involve social engineering and phishing attacks, which can be prevented through employee education and awareness programs.

Conclusion

Overall, the exploitation of the CVE-2026-20131 vulnerability by the Interlock group highlights the ongoing threat of ransomware attacks and the need for organizations to remain vigilant and proactive in their cybersecurity efforts.