Interlock Ransomware Exploits Cisco FMC Zero-Day CVE-2026-20131 — 31 Critical Vulnerabilities

The Interlock ransomware group has combined a previously unknown Cisco Firepower Management Center (FMC) zero-day with 31 additional critical vulnerabilities in a sophisticated campaign targeting financial institutions and healthcare organizations across North America and Europe.

The Zero-Day: CVE-2026-20131

• CVE: CVE-2026-20131
• CVSS Score: 9.9 (Critical)
• Component: Cisco Firepower Management Center web interface
• Type: Pre-authentication SQL injection leading to RCE
• Affected: FMC versions 7.2.x through 7.6.x
• Patch: Cisco Security Advisory cisco-sa-fmc-sqlinj-2026-3xBd

Attack Chain

Interlock’s attack methodology is unusually sophisticated, exploiting 31 vulnerabilities in a coordinated kill chain:

1. Initial access: CVE-2026-20131 — unauthenticated RCE on Cisco FMC
2. Lateral movement: Harvest credentials from FMC to access managed firewalls
3. Firewall manipulation: Create malicious access control policies to open internal networks
4. Active Directory attacks: Chain of 8 Windows vulnerabilities for domain admin
5. Data exfiltration: 2-3 weeks of quiet data collection before encryption
6. Ransomware deployment: Custom encryptor deployed across domain simultaneously

Patching Cisco FMC Immediately

# Check your FMC version
# FMC web GUI: Help > About

# Or via CLI
expert
sudo cat /etc/sf/ims.conf | grep -i version

# Update procedure
# 1. Download patch from Cisco.com (CCO account required)
# 2. System > Updates > Upload Update
# 3. Install the update (reboots required)

# Temporary mitigation — restrict FMC web access
# Allow only specific admin IPs to reach FMC on port 443
iptables -A INPUT -p tcp --dport 443 -s ADMIN_IP/32 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

Detecting Compromise

# Check FMC audit logs for suspicious queries
# FMC GUI: System > Monitoring > Audit

# Look for these IOCs in network logs
# Interlock C2 domains (from CISA advisory):
# update-cdn-service[.]com
# cisco-telemetry[.]net
# management-sync[.]org

# Check for unexpected firewall rule changes
# FMC > Policies > Access Control > Policy Changes log

Interlock Ransomware Group Profile

Interlock emerged in late 2023 and has grown rapidly to become one of the most active ransomware groups. Known characteristics:

• Dwell time of 18-45 days before encryption (longest in current threat landscape)
• Double extortion — steals data before encrypting
• Targets healthcare and financial sectors preferentially
• Average ransom demand: $2.8 million
• Believed to operate from Eastern Europe

The SudoFlare Takeaway

A ransomware group exploiting 31 vulnerabilities in a single campaign demonstrates that sophisticated threat actors are now operating with APT-level patience and capability. Firewall management systems are high-value targets because compromising them gives attackers control of an organization’s entire network perimeter. Treat FMC, Panorama, and FortiManager with the same security rigor as Active Directory domain controllers.