CVE-2026-20242

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.

CVSS v3 9.8 CRITICAL

9.8^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-javarce-y2NypXwk

Configurations

No configuration.

History

16 Sep 2026, 20:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-09-16 20:17

Updated : 2026-09-18 04:17

NVD link : CVE-2026-20242

Mitre link : CVE-2026-20242

CVE.ORG link : CVE-2026-20242

JSON object : View

Products Affected

No product.

CWE

CWE-502

Deserialization of Untrusted Data

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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.\r\nNotes:\r\n\r\nThis vulnerability can be exploited only by an attacker who has control of a host in the external database access list.\r\nIf the FMC management interface does not have public internet access, the attack surface that is associated with this vulnerability is reduced."}], "lastModified": "2026-09-18T04:17:34.083", "sourceIdentifier": "psirt@cisco.com"}