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CVE-2026-20131

Critical CVSS 10 Known exploited

Published 2026-03-04 · last changed 2026-06-17 · added to CISA KEV 2026-03-19

This one is being exploited in the wild.

CISA added CVE-2026-20131 to the Known Exploited Vulnerabilities catalog on 2026-03-19. Federal agencies are required to remediate it on a deadline. If you have affected machines, this is the class of finding that moves ahead of the rest of the queue.

The fix

We hold no Microsoft remediation data for CVE-2026-20131, which normally means it is not a Windows CVE. For non-Microsoft software the fix is the vendor's own updated release, and the affected versions are listed below.

What it is

A vulnerability in the web-based management interface of Cisco Secure Firewall Management Center (FMC) Software could allow an unauthenticated, remote attacker to execute arbitrary Java code as root on an affected device. This vulnerability is due to insecure deserialization of a user-supplied Java byte stream. An attacker could exploit this vulnerability by sending a crafted serialized Java object to the web-based management interface of an affected device. A successful exploit could allow the attacker to execute arbitrary code on the device and elevate privileges to root. Note: If the FMC management interface does not have public internet access, the attack surface that is associated with this vulnerability is reduced.

Sources

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