CVE-2026-20131
CRITICALCISA KEVEPSS 98th pctlDescription
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.
How to fix
Actively exploited, no published fix found yet
Federal remediation due: 2026-03-22
Known ransomware campaign use
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Exploit Intelligence
Very high risk: more likely to be exploited than 98% of all known CVEs.
Remediation due: 2026-03-22
Associated with ransomware campaigns
References
Related Vulnerabilities
Other CWE-502 (Deserialization of Untrusted Data) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2023-0669 | High | 7.2 | 100% | KEV + Ransom | Fix |
| CVE-2021-44228 | Critical | 10.0 | 100% | KEV + Ransom | Fix |
| CVE-2021-35464 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2023-29300 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2025-53770 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2022-41082 | High | 8.0 | 100% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2026-20131?
No published fix for CVE-2026-20131 has been found yet. It is on the CISA Known Exploited Vulnerabilities list; federal agencies must remediate by 2026-03-22. Apply the vendor's mitigations per CISA's guidance.
Is CVE-2026-20131 being actively exploited?
Yes. CVE-2026-20131 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. CISA has also linked it to known ransomware campaigns. US federal agencies were required to remediate it by 2026-03-22. Treat it as a priority whatever its CVSS score says.
How severe is CVE-2026-20131?
CVE-2026-20131 has a CVSS v3 base score of 10.0, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-03-25.