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Vulnerability record · CVE-2026-20242 · published 16 September 2026

CVE-2026-20242: Deserialization of untrusted data 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.

9.8 CVSS 3.1 Critical EPSS 0.64% · top 51.4% CWE-502 · Deserialization of untrusted data Awaiting Analysis
9.8CVSS 3.1 base score
0.64%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
1References
18 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

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

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Source: NIST National Vulnerability Database (record CVE-2026-20242), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.