CVE-2026-20340 Cisco Secure Firewall Management Center Software Deserialization Arbitrary Root Command Execution Vulnerability
Authenticated attackers can execute arbitrary root commands via unsafe deserialization in Cisco Secure Firewall Management Center.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-20340?
CVE-2026-20340 is a high-severity unsafe deserialization vulnerability in Cisco Secure Firewall Management Center (FMC), published on 16 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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).
Weakness: CWE-502
Which versions are affected by CVE-2026-20340?
How do I fix CVE-2026-20340?
No fix has been published for CVE-2026-20340 yet. Limit exposure of the affected software until one is available.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-20340 being exploited?
There is no known exploitation of CVE-2026-20340 in the wild and no public exploit code.
Sources
Also known as GHSA-xpr9-grjf-6fm6.