CriticalCVE-2026-20131

    Cisco Secure Firewall Management Center Software Remote Code Execution Vulnerability (CVE-2026-20131)

    Published In CISA KEV since Sources: pwn.watch, CVE.org, Cisco PSIRT, SingCERT, BSI

    What is affected, what to do

    This vulnerability stems from insecure deserialization (CWE-502) and allows an unauthenticated remote attacker to fully compromise affected systems with impact extending beyond the vulnerable component across confidentiality, integrity, and availability. The flaw is actively exploited in the wild and has been added to the CISA Known Exploited Vulnerabilities catalog, confirming real-world attacks. Confirmed use in ransomware campaigns significantly elevates the operational risk for any exposed organization. Immediate action is required: organizations should verify exposure and apply available patches without delay, treating this as a top-priority remediation item.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.0..7.0.0
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.0.1..7.0.0.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.1..7.0.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.1.0..7.1.0
    • Cisco Secure Firewall Management Center (FMC) eq 6.4.0.13..6.4.0.13
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.1.1..7.0.1.1
    • Cisco Secure Firewall Management Center (FMC) eq 6.4.0.14..6.4.0.14
    • Cisco Secure Firewall Management Center (FMC) eq 7.1.0.1..7.1.0.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.2..7.0.2
    • Cisco Secure Firewall Management Center (FMC) eq 6.4.0.15..6.4.0.15
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.0..7.2.0
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.2.1..7.0.2.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.3..7.0.3
    • Cisco Secure Firewall Management Center (FMC) eq 7.1.0.2..7.1.0.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.0.1..7.2.0.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.4..7.0.4
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.1..7.2.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.5..7.0.5
    • Cisco Secure Firewall Management Center (FMC) eq 6.4.0.16..6.4.0.16
    • Cisco Secure Firewall Management Center (FMC) eq 7.3.0..7.3.0
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.2..7.2.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.3.1..7.3.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.3..7.2.3
    • Cisco Secure Firewall Management Center (FMC) eq 7.1.0.3..7.1.0.3
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.3.1..7.2.3.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.4..7.2.4
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.6..7.0.6
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.4.1..7.2.4.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.5..7.2.5
    • Cisco Secure Firewall Management Center (FMC) eq 7.3.1.1..7.3.1.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.0..7.4.0
    • Cisco Secure Firewall Management Center (FMC) eq 6.4.0.17..6.4.0.17
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.6.1..7.0.6.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.5.1..7.2.5.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.1..7.4.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.6..7.2.6
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.1.1..7.4.1.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.6.2..7.0.6.2
    • Cisco Secure Firewall Management Center (FMC) eq 6.4.0.18..6.4.0.18
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.7..7.2.7
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.5.2..7.2.5.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.3.1.2..7.3.1.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.8..7.2.8
    • Cisco Secure Firewall Management Center (FMC) eq 7.6.0..7.6.0
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.2..7.4.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.8.1..7.2.8.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.6.3..7.0.6.3
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.2.1..7.4.2.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.9..7.2.9
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.7..7.0.7
    • Cisco Secure Firewall Management Center (FMC) eq 7.7.0..7.7.0
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.2.2..7.4.2.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.10..7.2.10
    • Cisco Secure Firewall Management Center (FMC) eq 7.6.1..7.6.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.2.3..7.4.2.3
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.8..7.0.8
    • Cisco Secure Firewall Management Center (FMC) eq 7.6.2..7.6.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.7.10..7.7.10
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.10.1..7.2.10.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.0.8.1..7.0.8.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.6.2.1..7.6.2.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.2.10.2..7.2.10.2
    • Cisco Secure Firewall Management Center (FMC) eq 7.7.10.1..7.7.10.1
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.2.4..7.4.2.4
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.3..7.4.3
    • Cisco Secure Firewall Management Center (FMC) eq 7.7.11..7.7.11
    • Cisco Secure Firewall Management Center (FMC) eq 7.6.4..7.6.4
    • Cisco Secure Firewall Management Center (FMC) eq 10.0.0..10.0.0
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.4..7.4.4
    • Cisco Secure Firewall Management Center (FMC) eq 7.4.5..7.4.5

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    10.0

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    10.0

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: pwn.watch, CVE.org, Cisco PSIRT, SingCERT, BSI

    43.2 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 98.7

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    267.87 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    10.0 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    10.0
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    43.2 %
    Elevated — model estimates 10-50% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    98.7
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-502

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication, needs no user interaction and yields root code execution with a scope change. The asset compromised is the central control plane for the entire perimeter firewall estate. CISA flags known ransomware campaign use, and the exploitation likelihood is among the highest of all scored CVEs, which points to broad scanning and mature exploit tooling. Typical victims are organisations whose FMC management interface is internet-facing. A hijacked FMC lets attackers rewrite firewall policy, harvest credentials and quietly open paths inward ahead of encryption. For KRITIS/NIS2 entities, treat any exposed FMC as critical: act immediately and assume compromise. A strictly segmented FMC is still high priority but can be patched in the next short-notice maintenance window.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Cut exposure first: Check whether the FMC web management interface (HTTPS, TCP 443 by default) is reachable from the internet or from user VLANs. If it is, immediately restrict access via upstream firewall/ACL to a dedicated management network or jump-host allowlist. Closing external exposure takes priority over everything else.
      • Inventory affected versions: Check every FMC instance (hardware appliance and FMCv) against the affected releases, which include 6.4.0.13, 6.4.0.14, 7.0.0, 7.0.0.1, 7.0.1, 7.0.1.1, 7.1.0 and 7.1.0.1. The Cisco Security Advisory has the full list of affected and fixed versions. Cisco Security Cloud Control (SCC) Firewall Management is cloud-delivered; confirm remediation status with Cisco or in your SCC tenant.
      • Apply the fix: A patch is available from the vendor — look up the fixed release in the Cisco advisory. Upgrade internet-exposed FMCs first. Check legacy trains such as 6.4.x for support status and the supported upgrade path.
      • Assess for compromise before patching: If the management interface was exposed, treat the appliance as potentially compromised. Preserve logs and configuration backups before upgrading or rebooting. Patching does not remove persistence an attacker may already have established.
      • Rotate secrets: If compromise is suspected, rotate every secret stored on the FMC. This covers local admin accounts, LDAP/AD bind and RADIUS shared secrets, REST API credentials, managed-device registration keys, and VPN pre-shared keys and certificates. Root-level code execution gives full access to all of them.
      • Review managed devices: On every FTD managed by an affected FMC, check recently deployed policies for unauthorised changes. Look for new allow rules, NAT changes, VPN profiles or modified admin accounts.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Make the FMC management port (TCP 443) reachable only from a dedicated admin VLAN or PAW/jump hosts, and drop everything else via ACL. Restrict the sftunnel to managed devices (TCP 8305) to known FTD management IPs.
      • Egress filtering for the FMC: Allowlist outbound traffic from the FMC appliance to required destinations only: Cisco update servers, NTP, DNS, syslog/SIEM, LDAP and managed devices. This breaks reverse shells and second-stage downloads after a successful deserialisation exploit.
      • IPS/WAF in front of the management interface: Where the interface sits behind a reverse proxy or IPS segment, block HTTP requests carrying Java serialisation markers. These include the magic bytes AC ED 00 05 in the body, the base64 prefix rO0AB, and Content-Type: application/x-java-serialized-object. Enable current Cisco Talos/Snort coverage for CVE-2026-20131 where available.
      • Harden the admin access path: Allow administrative access only via MFA-protected VPN followed by a jump host. Never publish the management interface through port forwarding or static NAT.
      • IAM/least privilege: Reduce the directory permissions of service accounts used by the FMC (LDAP bind, integrations) to minimal read access. This limits the blast radius of credential theft.

    3. Runbook step 3

      Detection rules

      • Serialised Java objects in web traffic: Hunt proxy, WAF or Zeek HTTP logs for POST requests to the FMC whose body or headers contain rO0AB, aced0005 or application/x-java-serialized-object. Suricata shape: content:"|AC ED 00 05|"; http_client_body; scoped to the FMC destination IP. Requests from sources outside the admin network are especially suspicious.
      • Process ancestry on the appliance: A Java/Tomcat process spawning sh, bash, curl, wget, python, perl or nc is highly anomalous on an FMC. Where appliance syslog or audit telemetry is available, use this Sigma shape: ParentImage|endswith: '/java' AND Image|endswith: ['/sh','/bash','/curl','/wget'].
      • Network telemetry: Review Zeek conn.log or NetFlow for outbound connections from the FMC IP to non-allowlisted external destinations. Example SPL: index=netflow src_ip=<FMC_IP> NOT dest_ip IN (<allowlist>) | stats count by dest_ip, dest_port.
      • FMC audit log and configuration drift: In the FMC audit log or SIEM syslog feed, alert on new local users, role changes and unexpected policy deployments. Also alert on access-rule, NAT or VPN modifications and on logins outside change windows.
      • Downstream activity: Watch for LDAP/AD authentications by the FMC bind account from unusual source IPs (Windows Event ID 4624/4625 for that service account). Also flag new VPN sessions using unfamiliar profiles.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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&nbsp;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.

    Source: pwn.watch, NVD (NIST), CISA KEV Catalog, cvelistv5, cisco_csaf, CVE.org (MITRE), CSA/SingCERT, BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    CiscoCisco Secure Firewall Management Center (FMC)
    • 7.4.1.1
    • 7.2.10.2
    • 7.4.2.4
    • 7.4.2.3
    • 7.2.2
    • 7.6.0
    • 6.4.0.13
    • 7.3.0
    • 7.1.0
    • 7.4.2.1
    • 7.2.5
    • 7.0.6
    • 7.4.0
    • 7.0.2
    • 7.1.0.1
    • 7.0.5
    • 7.6.2
    • 7.0.6.1
    • 7.4.5
    • 7.2.8.1
    • 7.3.1.1
    • 7.3.1
    • 7.0.6.2
    • 6.4.0.18
    • 7.0.4
    • 7.6.4
    • 7.3.1.2
    • 7.2.7
    • 7.0.1.1
    • 7.6.1
    • 7.2.10.1
    • 7.2.4
    • 7.1.0.3
    • 7.0.3
    • 7.2.1
    • 7.2.6
    • 7.2.8
    • 7.0.0.1
    • 7.0.0
    • 7.7.0
    • 7.2.3.1
    • 7.2.4.1
    • 7.2.3
    • 7.6.2.1
    • 7.7.11
    • 7.4.1
    • 10.0.0
    • 6.4.0.17
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    Vendors and products

    Weakness classes (CWE)

    • CWE-502Deserialization of Untrusted Data

      Base

      The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

      Entry at MITRE CWE-502

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    PoC-in-GitHub (nomi-sec)CVE-2026-20131-Post-Incident-Written-Report (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • sec.cloudapps.cisco.comcisco-sa-fmc-rce-NKhnULJhVendor advisory, pwn-watch
    • aws.amazon.comblogs/security/amazon-threat-intelligence-teams-identify-interl…Third-party advisory, Technical description
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-20131government-resource, US government resource
    • cert.atCERT.at: Kritische Sicherheitslücken in Cisco Secure Firewall Produkten - Updates verfügbarcert-at
    • pwn.watchpwn.watch: Cisco Secure Firewall Management Center (FMC): Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Managementpwn-watch
    • NVD (NIST)NVD: CVE-2026-20131pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Linked advisories

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