CISA KEV Critical Insecure deserialization

CVE-2026-20131 — Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management Deserialization of Untrusted Data Vulnerability

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.

Published Mar 4, 2026 · Updated Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, CVE Program (cve.org) e CISA ADP, NIST National Vulnerability Database, GitHub Security Advisories · CNA: cisco

Urgent

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Mar 19, 2026 R used by ransomware (CISA) Proofs of concept on GitHub · 5

How the score was calculated

Confirmed exploitation (CISA KEV)+35
Used in ransomware campaigns (CISA)+10
Public exploit/PoC (github)+6
EPSS 43.2% (30-day exploitation probability)+15
Technical severity (critical)+10
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Confirmed

CISA KEV, listed Mar 19, 2026

EPSS FIRST

43.17%

ahead of 99% of scored CVEs · Oct 14, 2026

Affects

Cisco

Cisco Secure Firewall Management Center (FMC) and 1 more

CVSS base

10.0

Critical · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Active

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

US federal deadline: Mar 22, 2026 — passed 207 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Cisco Cisco Secure Firewall Management Center (FMC), Cisco Secure Firewall Management Center).
Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
EPSS ahead of 99% of scored CVEs: prioritize it in the patch queue.
Search available logs for exploit probes matching the vulnerability class (insecure deserialization), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Cisco	Cisco Secure Firewall Management Center (FMC)	version 7.7.10version 7.4.5version 7.4.4version 10.0.0version 7.6.4version 7.7.11version 7.4.3version 7.4.2.4 and 62 more version 7.7.10.1version 7.2.10.2version 7.6.2.1version 7.0.8.1version 7.2.10.1version 7.2.8.1version 7.6.2version 7.0.8version 7.4.2.3version 7.6.1version 7.2.10version 7.4.2.2version 7.7.0version 7.0.7version 7.2.9version 7.4.2.1version 7.0.6.3version 7.0.0version 7.0.0.1version 7.0.1version 7.1.0version 6.4.0.13version 7.0.1.1version 6.4.0.14version 7.1.0.1version 7.0.2version 6.4.0.15version 7.2.0version 7.0.2.1version 7.0.3version 7.1.0.2version 7.2.0.1version 7.0.4version 7.2.1version 7.0.5version 6.4.0.16version 7.3.0version 7.2.2version 7.3.1version 7.2.3version 7.1.0.3version 7.2.3.1version 7.2.4version 7.0.6version 7.2.4.1version 7.2.5version 7.3.1.1version 7.4.0version 6.4.0.17version 7.0.6.1version 7.2.5.1version 7.4.1version 7.2.6version 7.4.1.1version 7.0.6.2version 6.4.0.18version 7.2.7version 7.2.5.2version 7.3.1.2version 7.2.8version 7.6.0version 7.4.2	Vulnerable	CVE Program (cve.org) e CISA ADP
Cisco	Secure Firewall Management Center	version 6.4.0.13version 6.4.0.14version 6.4.0.15version 6.4.0.16version 6.4.0.17version 6.4.0.18version 7.0.0version 7.0.0.1 and 63 more version 7.0.1version 7.0.1.1version 7.0.2version 7.0.2.1version 7.0.3version 7.0.4version 7.0.5version 7.0.6version 7.0.6.1version 7.0.6.2version 7.0.6.3version 7.0.7version 7.0.8version 7.0.8.1version 7.1.0version 7.1.0.1version 7.1.0.2version 7.1.0.3version 7.2.0version 7.2.0.1version 7.2.1version 7.2.2version 7.2.3version 7.2.3.1version 7.2.4version 7.2.4.1version 7.2.5version 7.2.5.1version 7.2.5.2version 7.2.6version 7.2.7version 7.2.8version 7.2.8.1version 7.2.9version 7.2.10version 7.2.10.1version 7.2.10.2version 7.3.0version 7.3.1version 7.3.1.1version 7.3.1.2version 7.4.0version 7.4.1version 7.4.1.1version 7.4.2version 7.4.2.1version 7.4.2.2version 7.4.2.3version 7.4.2.4version 7.4.3version 7.4.4version 7.4.5version 7.6.0version 7.6.1version 7.6.2version 7.6.2.1version 7.6.3version 7.6.4version 7.7.0version 7.7.10version 7.7.10.1version 7.7.11version 10.0.0	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
10.0	CVSS 3.1	Critical	3.9	6.0	psirt@cisco.com via NIST National Vulnerability Database
10.0	CVSS 3.1	Critical	—	—	GitHub, Inc. via GitHub Security Advisories
10.0	CVSS 3.1	Critical	—	—	cisco via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (score shown at the top: psirt@cisco.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-502 · Deserialization of Untrusted Data

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed

Mar 19, 2026

Federal deadline

Mar 22, 2026

passed 207 day(s) ago

Ransomware use

Known

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Proofs of concept on GitHub

sak110/CVE-2026-20131 ★ 3 Mar 11, 2026
Originally a Honeypot for CVE-2026-20131 ★ 2 Apr 7, 2026
p3Nt3st3r-sTAr/CVE-2026-20131-POC ★ 0 Mar 6, 2026
CVE-2026-20131 ★ 0 May 10, 2026
Post-incident report on CVE-2026-20131 (CVSS 10.0), a Cisco FMC insecure deserialization vulnerability exploited by Interlock ransomware. Details root-cause analysis, lateral movement tactics, and emergency containment strategies. ★ 0 Aug 28, 2026

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 43.17%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Monitor serialized objects in requests and unexpected processes spawned by the runtime.
Hunt retroactively in logs from before Mar 19, 2026 (KEV listing): exploitation may have started earlier.

web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)application logs

Timeline

What happened to this CVE, newest first.

2026
Affected products added · cisco/secure firewall management center
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · Published → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record published
Oct 13, 2026
Affected products added · cisco/cisco secure firewall management center (fmc)
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
CVSS changed · 10.0
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Source status changed · → Published
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Added to CISA KEV (detected)
Oct 13, 2026 · CISA Known Exploited Vulnerabilities
Record created in this database
Oct 13, 2026 · CISA Known Exploited Vulnerabilities
Added to CISA KEV catalog
Mar 18, 2026 · CISA
CVE published
Mar 4, 2026 · cisco

Source activity

Repeated readings are counted rather than listed.

3× References added · Oct 13, 2026 – Oct 13, 2026
1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

6 on the record

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-rce-NKhnUL
Vendor Advisory, CVE Program (cve.org) e CISA ADP
www.cisa.gov/known-exploited-vulnerabilities-catalog
US Government Resource, NIST National Vulnerability Database
nvd.nist.gov/vuln/detail/CVE-2026-20131
GitHub Security Advisories
aws.amazon.com/blogs/security/amazon-threat-intelligence-teams-identify-interlock-ra
GitHub Security Advisories
aws.amazon.com/blogs/security/amazon-threat-intelligence-teams-identify-interlock-ra
Technical Description, NIST National Vulnerability Database
github.com/advisories/GHSA-r229-mj76-g2qx
GitHub Security Advisories

Elsewhere on this site

Cisco
every CVE for this vendor

2026-03
what else CISA listed that month

Insecure deserialization
same class

CWE-502
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-20316 Cisco Secure Firewall Management Center Use of Hard-coded Password Vulnerability KEV Jul 29, 2026
Critical CVE-2026-20079 Cisco Firewall Management Center Authentication Bypass Using an Alternate Path or Channel Vulnerability KEV Mar 4, 2026
Medium CVE-2026-20044 Cisco Secure Firewall Management Center Command Injection Vulnerability Mar 4, 2026
Medium CVE-2026-20018 Cisco Firepower Management Center Software and Firepower Threat Defense Path Traversal Vulnerability Mar 4, 2026
High CVE-2026-20002 SQL Injection in Cisco Secure Firewall Management Center Mar 4, 2026
Medium CVE-2026-20003 SQL Injection in Cisco Secure Firewall Management Center Mar 4, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-20131 is "Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management Deserialization of Untrusted Data Vulnerability", rated Critical. It affects Cisco Secure Firewall Management Center (FMC) (Cisco); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 10.0 describes technical severity. EPSS 43.17% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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