Known exploited · Cisco
CVE-2026-20131: Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management Deserialization of Untrusted Data Vulnerability
What it is
Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management contain a deserialization of untrusted data vulnerability in the web-based management interface that could allow an unauthenticated, remote attacker to execute arbitrary Java code as root on an affected device.
- Vendor
- Cisco
- Product
- Secure Firewall Management Center (FMC)
- Added to KEV
- March 19, 2026
- CISA due date
- March 22, 2026
- Ransomware use
- Known
What CISA requires
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Forensic triage
No
What to do now
- Find every instance of Secure Firewall Management Center (FMC) you run, including the forgotten ones, and check its version against the vendor advisory.
- Apply the vendor's fix or mitigation, before March 22, 2026 if you are bound by CISA's deadline, sooner if it faces the internet.
- Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
- Until every instance is patched, block the attack at the edge: a WAF in blocking mode stops Java deserialization payloads.
References
The Dome
Block it at the edge while you patch
The Dome's WAF runs the OWASP Core Rule Set in blocking mode and stops Java deserialization payloads before they reach your application.
See the DomeT Academy
Train the engineers who fix it
Security engineering on real hosts in the browser, every objective checked on the machine. The first two lessons of Linux 1 are free.
Start freeSource: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.