CVE-2026-20316: Cisco FMC Hardcoded Password Gives Unauthenticated Remote Access

Executive Summary

A hardcoded static password embedded in Cisco Secure Firewall Management Center (FMC) Software allows an unauthenticated, remote attacker to log in using a low-privileged account that exists in every affected installation. The vulnerability, tracked as CVE-2026-20316 (CWE-259, CVSS 5.3 Medium), was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on July 29, 2026, with a mandatory federal remediation deadline of August 1, 2026.

Despite its medium CVSS score, Cisco internally classifies this flaw as High severity because the access it grants can be chained with other FMC vulnerabilities to achieve full management-plane control over enterprise firewall deployments.

Vulnerability Overview

Root Cause

Cisco FMC ships with a static, low-privileged account whose credentials are hardcoded into the software image. Because the account exists in every installation and cannot be disabled through normal configuration, any attacker who discovers the credentials can authenticate remotely and access sensitive platform data without any prior knowledge of the target environment.

The advisory is tracked under Cisco identifier cisco-sa-fmc-static-cred-BET3Cjh.

Why This Is More Dangerous Than Its CVSS Score Suggests

CVSS 5.3 reflects what the hardcoded credential gives you directly: authenticated, low-privileged remote access to sensitive data. However, Cisco's own advisory rates the real-world severity as High for a critical reason: chaining.

FMC is the centralized management platform for Cisco Secure Firewall and Firepower appliances across enterprise networks. Gaining even low-privileged access to FMC provides:

• Firewall policy visibility — an attacker can read existing rules to identify gaps for subsequent lateral movement
• Pivot credentials — FMC sessions and configurations may expose credentials for managed firewalls
• Chaining surface — the initial access can be combined with other FMC vulnerabilities (privilege escalation, path traversal) to gain full management-plane control

In short: the device that controls the firewalls now has an unlocked back door. For organizations where FMC manages hundreds of firewalls, the blast radius of a successful chain attack is enormous.

Affected Versions

Consult the Cisco security advisory for exact fixed versions.

Exploitation Status

CISA's KEV listing on July 29, 2026 confirms active exploitation in the wild. The three-day remediation window (July 29 → August 1) is aggressive by CISA standards, reflecting the urgency of the confirmed threat activity. Automated exploitation is considered feasible given the simplicity of using a known static credential.

Immediate Remediation Steps

1. Patch Immediately

Apply the fixed FMC version corresponding to your deployment from Cisco's advisory. This is the only complete fix — there is no workaround that disables the hardcoded account.

2. Audit for Compromise

If your FMC version falls within the affected range, treat your environment as potentially compromised:

• Review FMC authentication logs for unexpected logins, especially from external IPs
• Look for logins from the low-privileged static account against the timestamps of known-vulnerable exposure windows
• Audit firewall policy changes made via FMC over the past 30–90 days

3. Network Segmentation

If patching is not immediately possible:

• Restrict FMC management interface access — limit to known admin IP ranges via ACLs or firewall rules
• Block external access to the FMC web interface and REST API
• Monitor for authentication attempts from unexpected sources

4. Federal Agency Compliance

FCEB agencies must apply patches or implement mitigations by August 1, 2026, per CISA's Binding Operational Directive 22-01.

Key Takeaways

1. Hardcoded credentials in a firewall management platform — the device meant to secure your network ships with a static back door
2. CVSS 5.3 understates risk — chaining with other FMC vulns elevates real-world severity to High
3. Active exploitation confirmed — CISA's aggressive 3-day KEV deadline reflects urgency
4. No authentication required — any internet-exposed FMC is vulnerable without additional network controls
5. Patch immediately — no workaround exists; only the fixed version removes the hardcoded credential

References

• Cisco Security Advisory: cisco-sa-fmc-static-cred-BET3Cjh
• NVD — CVE-2026-20316
• CISA Known Exploited Vulnerabilities Catalog
• CISA BOD 22-01 — Reducing the Significant Risk of Known Exploited Vulnerabilities