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CVE-2026-20340

Cisco Secure Firewall Management Center Software Deserialization Arbitrary Root Command Execution Vulnerability

Published: Sep 16, 2026Updated: Sep 18, 2026 Sources: CVE List NVDCWE-502
8.8HIGH
NVD MITRE
EPSS Score
0.7%
Top 48.5%
CISA KEV
Not in KEV
Exploits
0 Known
Remediation
No Fix Available
Self-Check
Not available

Description

A vulnerability in Cisco Secure FMC Software could allow an authenticated, remote attacker to execute arbitrary commands at the root privilege level. This vulnerability is due to unsecured deserialization of web-management user-controlled data. An attacker could exploit this vulnerability by authenticating to the device and sending a crafted HTTP payload. A successful exploit could allow the attacker to save the crafted payload and then execute it on the underlying operating system as root. To exploit this vulnerability, the attacker must have valid credentials for a user account with at least the role of Security Analyst (read-only).

In plain language

AI Act now

Cisco Secure Firewall Management Center has a serious flaw that lets a logged-in low-privilege user take full control; treat it as urgent, but no vendor fix information is available yet.

Executive summary

Authenticated remote root command execution in Cisco Secure Firewall Management Center through insecure deserialization of attacker-controlled web-management data, requiring Security Analyst-or-higher credentials.

If affected, business impact
Full firewall management takeoverNetwork policy changesSecurity monitoring disruptionCustomer data exposureOperational outage

What to do now

  1. Check whether your organization runs Cisco Secure Firewall Management Center and identify accounts assigned the Security Analyst role or higher.
  2. No fixed version has been published in the available findings; ask Cisco or your support provider for the official remediation and deployment timeline.
  3. Until a fix is available, restrict access to the management interface to trusted administrator networks and remove unnecessary Security Analyst accounts.
  4. Review management-system logs for unusual account activity, unexpected commands, or unfamiliar configuration changes.
May need vendor / contractor work

CVSS Vector Breakdown

AV:NAC:LPR:LUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
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Weaknesses

CWE-502

Affected Products

Cisco
commercial·USaka cisco systems, cisco systems inc.
Cisco Secure Firewall Management Center (FMC)
Networking Infrastructure

Exploitability

0 exploit sources identified

Exploit details including PoC links, Metasploit modules, and scanner templates are available after registration.

View exploit details
Is your org exposed to CVE-2026-20340?Request an assessment to establish which checks are appropriate for your systems. Check my exposure

Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

3 techniques
Execution
Initial Access
View detailed technique mapping

References

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-mulivulns-4PsnFwvx
sec.cloudapps.cisco.com
News mentions
1

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