Interlock Ransomware Exploits Cisco FMC Zero-Day in Global Attacks

Executive Summary

The Interlock ransomware group is actively exploiting a zero-day vulnerability in Cisco Firepower Management Center (FMC) to gain initial access to target networks, according to analysis by Recorded Future's Insikt Group. The activity was identified as part of a broader March 2026 vulnerability landscape report, which documented a 139% monthly increase in high-impact vulnerabilities requiring immediate remediation, rising from 13 in February to 31 in March.

Technical Analysis

Recorded Future's research indicates threat actors, specifically the Interlock ransomware operation, are leveraging an unpatched flaw in Cisco FMC software. The exact mechanism of the vulnerability is not detailed in the public summary, but its classification as a zero-day indicates it was exploited before a patch was available from the vendor. The Firepower Management Center is a central console for managing Cisco's next-generation firewalls, and compromise could provide attackers with deep network visibility and control. The report does not specify whether Cisco has since issued a patch or assigned a CVE ID for this flaw.

Tactics, Techniques & Procedures

The primary TTP identified is the exploitation of a public-facing application vulnerability (likely corresponding to MITRE ATT&CK technique T1190) for initial access. By targeting the Cisco FMC, the actors aim to bypass perimeter security controls. The subsequent deployment of Interlock ransomware suggests follow-on techniques for lateral movement, privilege escalation, and data encryption.

Threat Actor Context

The threat actor is identified as the Interlock ransomware group. The source material does not provide further details on the group's origins, typical targets, or ransom tactics. The group's name does not correspond to a widely reported ransomware operation as of early 2026, suggesting it may be a newer or rebranded entity. Its choice to exploit a network security appliance zero-day indicates a focus on enterprise environments and a capability to weaponize high-value vulnerabilities quickly.

Mitigations & Recommendations

Organizations using Cisco Firepower Management Center should immediately consult Cisco's security advisories for the most recent patches and updates. As a critical network management component, FMC should not be exposed directly to the internet. If internet-facing access is required, it must be protected with strict access controls, multi-factor authentication, and placed behind a VPN. Network monitoring for anomalous activity originating from or targeting the FMC appliance is advised. Recorded Future's broader recommendation, based on the surge in high-impact flaws, is to prioritize remediation of vulnerabilities based on active exploitation and criticality to the business, rather than relying solely on CVSS scores.