Cisco Secure Firewall Management Center login.cgi Authentication Bypass Vulnerability

August 11th, 2026
ZDI-26-533 ZDI-CAN-30390

CVE ID

CVE-2026-20316

CVSS Score

9.8 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors

Cisco

Affected Products

Secure Firewall Management Center

Vulnerability Details

This vulnerability allows remote attackers to bypass authentication on affected installations of Cisco Secure Firewall Management Center. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the login.cgi endpoint. The issue results from improper implementation of the authentication algorithm. An attacker can leverage this vulnerability to bypass authentication on the system.

Additional Details

Cisco has issued an update to correct this vulnerability. More details can be found at:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-static-cred-BET3Cjh

Disclosure Timeline

  • 2026-04-16 - Vulnerability reported to vendor
  • 2026-08-11 - Coordinated public release of advisory
  • 2026-08-11 - Advisory Updated

Credit

Andy Niu of TrendAI Research

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