CVE-2026-20079

Critical

Published: 04 March 2026

Published

04 March 2026

Modified

05 March 2026

KEV Added

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Patch

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CVSS Score 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS Score 0.1228 93.9th percentile

Risk Priority 27 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-20079 is a critical-severity Authentication Bypass Using an Alternate Path or Channel (CWE-288) vulnerability in Cisco Secure Firewall (inferred from references). Its CVSS base score is 10.0 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 6.1% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly mitigates the CVE by requiring timely remediation of the authentication bypass flaw through patching affected FMC software versions.

AC-3 Access Enforcement good match

prevent

Enforces approved authorizations for access to the web interface, preventing unauthenticated attackers from bypassing authentication to execute scripts and gain root access.

SI-10 Information Input Validation good match

prevent

Validates crafted HTTP inputs to the web interface, blocking the exploitation vector that triggers the improper boot-time process leading to root access.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1068 Exploitation for Privilege Escalation Privilege Escalation

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.

attack.mitre.org →

Why these techniques?

The vulnerability enables unauthenticated remote attackers to exploit the public-facing web interface (T1190) for arbitrary script execution and root access, directly facilitating exploitation for privilege escalation (T1068).

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD Description

A vulnerability in the web interface of Cisco Secure Firewall Management Center (FMC) Software could allow an unauthenticated, remote attacker to bypass authentication and execute script files on an affected device to obtain root access to the underlying operating system.…

This vulnerability is due to an improper system process that is created at boot time. An attacker could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute a variety of scripts and commands that allow root access to the device.

Deeper analysisAI

CVE-2026-20079 is a critical authentication bypass vulnerability (CVSS 10.0) in the web interface of Cisco Secure Firewall Management Center (FMC) Software. The issue stems from an improper system process created at boot time, which allows an unauthenticated, remote attacker to bypass authentication mechanisms and execute arbitrary script files on an affected device, ultimately granting root access to the underlying operating system. This flaw is classified under CWE-288.

An unauthenticated, remote attacker can exploit this vulnerability by sending crafted HTTP requests to the web interface of a vulnerable FMC device. Successful exploitation enables the attacker to execute a variety of scripts and commands, providing full root-level control over the device, including potential data exfiltration, modification of configurations, or further lateral movement within the network.

For mitigation details, including affected versions and patch information, refer to the Cisco Security Advisory at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-onprem-fmc-authbypass-5JPp45V2.