CVE-2026-20242: Cisco Secure Firewall Management Center Software Java Deserialization Remote Code Execution Vulnerability
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
Reduce exposure by ensuring the Cisco Secure Firewall Management Center (FMC) management interface does not have public internet access.
- Compensating control
Restrict the external database access list so only required and trusted hosts are included, since the vulnerability can be exploited only by an attacker who controls a host in the external database access list.
Event History
Frequently Asked Questions
Who can exploit this vulnerability in practice?
Exploitation requires control of a host that is configured in the FMC External Database Access list. The attacker can then send a crafted serialized Java byte stream to a specific TCP port on the affected FMC device.
Does an attacker need credentials or user interaction?
No. The vulnerability is exploitable remotely without authentication or user interaction, provided the attacker controls a host in the external database access list.
How severe is successful exploitation?
A successful exploit allows arbitrary command execution on the affected device and can result in root privileges. It affects confidentiality, integrity, and availability.
What reduces exposure if remediation cannot happen immediately?
Restrict access to the FMC management interface, particularly preventing public internet access. Review the External Database Access list and limit it to trusted, controlled hosts, because exploitation depends on control of a listed host.