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Unlock with Pro - from £29/user/moDetect Cisco Secure Firewall Management Center Hard-coded Credential Exploitation (CVE-2026-20316) in Google Chronicle
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
YARA-L Detection Query
rule cisco_fmc_hardcoded_cred_login {
meta:
author = "df00tech"
description = "Detects login to Cisco FMC using accounts associated with hard-coded credential CVE-2026-20316"
severity = "CRITICAL"
events:
$login.metadata.event_type = "USER_LOGIN"
$login.principal.application = "Cisco Secure Firewall Management Center"
$login.target.user.userid = /(?i)(admin|support|maintenance|cisco|root|backdoor)/
condition:
$login
}Chronicle YARA-L rule identifying user login events on Cisco FMC using account names consistent with hard-coded credential abuse tied to CVE-2026-20316.
Data Sources
Required Tables
False Positives & Tuning
- Standard admin logins by verified staff
- Automated support account logins during patch cycles
- Test/lab environment logins using default 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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