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Unlock with Pro - from £29/user/moDetect Cisco Secure Firewall Management Center Hard-coded Credential Exploitation (CVE-2026-20316) in Microsoft Sentinel
Detects exploitation attempts and successful authentication against Cisco Secure Firewall Management Center (FMC) using an undocumented, hard-coded static credential (CVE-2026-20316, CWE-259). This flaw is listed in CISA KEV and has been exploited in zero-day attacks per Cisco and public reporting. Detection focuses on FMC authentication logs, management-interface access from unexpected sources, and post-authentication administrative actions consistent with abuse of a built-in account.
MITRE ATT&CK
KQL Detection Query
// Requires Cisco FMC/Secure Firewall syslog ingested via CommonSecurityLog or custom table
CommonSecurityLog
| where DeviceVendor == "Cisco" and DeviceProduct has_any ("Firewall Management Center", "FMC", "Secure Firewall")
| where Activity has_any ("Login", "Authentication", "auth")
| extend AccountName = tostring(SourceUserName)
| where AccountName has_any ("admin", "support", "maintenance", "cisco", "root", "backdoor")
| summarize LoginCount = count(), SourceIPs = make_set(SourceIP), FirstSeen = min(TimeGenerated), LastSeen = max(TimeGenerated) by AccountName, DeviceName, DestinationIP
| where LoginCount >= 1
| order by LastSeen descFlags authentication events against Cisco FMC management interfaces using built-in or maintenance-style accounts that may correspond to the hard-coded credential documented in CVE-2026-20316.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate use of documented maintenance/support accounts by authorized administrators
- Automated backup or health-check scripts using service accounts with similar naming
- Third-party monitoring tools authenticating via SNMP/API with generic account names
Other platforms for CVE-2026-20316
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate FMC Login with Generic Maintenance Account Name
Expected signal: HTTP POST authentication request logged in FMC syslog/audit log with account name 'maintenance' and source IP of the lab test host.
- Test 2Simulate Repeated Login Attempts from Multiple Source IPs
Expected signal: Multiple authentication log entries for account 'admin' with distinct source IP addresses within a short time window.
- Test 3Simulate Post-Login Configuration Change
Expected signal: FMC audit log entry showing policy creation/modification action correlated with the prior simulated login session.
References (5)
- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-static-cred-BET3Cjh
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-20316
- https://www.bleepingcomputer.com/news/security/cisco-warns-of-fmc-static-credential-flaw-exploited-in-zero-day-attacks/
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