CVE-2026-20242 Cisco Secure Firewall Management Center Software Java Deserialization Remote Code Execution Vulnerability
Unauthenticated remote attackers can execute arbitrary commands as root via insecure Java deserialization in Cisco FMC if they control a host in the external database access list.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-20242?
CVE-2026-20242 is a critical unsafe deserialization vulnerability in Cisco Secure Firewall Management Center (FMC), published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A vulnerability in the External Database Access feature of Cisco Secure Firewall Management Center (FMC) Software could allow an unauthenticated, remote attacker to execute arbitrary commands as root on an affected device. This vulnerability is due to insecure deserialization of a user-supplied Java byte stream from a host that is configured in the external database access list. An attacker could exploit this vulnerability by sending a crafted, serialized Java byte stream to a specific TCP port of an affected device. A successful exploit could allow the attacker to execute arbitrary commands on the device and elevate privileges to root. Notes: This vulnerability can be exploited only by an attacker who has control of a host in the external database access list. If the FMC management interface does not have public internet access, the attack surface that is associated with this vulnerability is reduced.
Weakness: CWE-502
Which versions are affected by CVE-2026-20242?
How do I fix CVE-2026-20242?
No fix has been published for CVE-2026-20242 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-2026-20242 being exploited?
There is no known exploitation of CVE-2026-20242 in the wild and no public exploit code.
Sources
Also known as GHSA-mgpv-rwhr-9mx2.