CVE-2026-20316: Hard-coded Credential in Cisco Secure Firewall Management Center Actively Exploited (CISA KEV)

What Happened

CVE-2026-20316 is a hard-coded credential vulnerability (CWE-259) in Cisco Secure Firewall Management Center (FMC). The root cause is an undocumented, static credential built into the product that allows an attacker who knows or discovers it to authenticate to the FMC management interface as a legitimate, likely privileged, account — bypassing normal authentication controls entirely. Because the credential is static and not tied to any individual deployment's configured secrets, exploitation does not require prior compromise of user credentials, phishing, or brute-forcing; possession of the hard-coded value is sufficient. Successful exploitation grants an attacker administrative access to the FMC, which centrally manages Cisco Secure Firewall (formerly Firepower) sensors — a foothold with significant downstream impact on network security policy and visibility.

Affected Software

• Vendor: Cisco
• Product: Secure Firewall Management Center (FMC)

Specific affected version ranges were not provided in the source detection data; organizations running FMC should consult Cisco's advisory directly to confirm exposure and available fixes.

Exploitation Status

This vulnerability is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and, per Cisco and public reporting, has been exploited in zero-day attacks — meaning active exploitation was observed before or independent of a public patch or advisory being available. For defenders, this elevates the vulnerability from theoretical risk to an immediate, real-world threat: FMC deployments should be treated as a priority remediation and monitoring target, particularly for management-interface exposure to the internet or untrusted network segments.

How Our Detection Catches It

Our detection focuses on three complementary signal sources rather than a single indicator, since hard-coded credential abuse can otherwise blend in with legitimate administrative activity:

• FMC authentication logs — surfacing successful and failed authentication events tied to the built-in account, including anomalous authentication patterns inconsistent with normal admin usage.
• Management-interface access from unexpected sources — flagging connections to the FMC management plane originating from source IPs, networks, or geographies that fall outside expected administrative access patterns.
• Post-authentication administrative actions — correlating successful logins with subsequent configuration changes or administrative operations consistent with abuse of the built-in account, helping distinguish exploitation from benign access.

This logic is shipped across our full SIEM coverage matrix, including Microsoft Sentinel (KQL), Splunk (SPL), Elastic (EQL), IBM QRadar (AQL), Sumo Logic, Google Chronicle (YARA-L), and CrowdStrike (CQL), so teams can deploy consistent detection logic regardless of their SIEM stack.

Get the Full Detection

For the complete detection queries across all supported platforms, MITRE ATT&CK mapping, and deployment guidance, see the full detection page for CVE-2026-20316 on df00tech.