CVE-2026-20343

Cisco Secure Firewall Management Center Software Information Disclosure and Disk Denial of Service Vulnerability

No known exploitation. EPSS puts it in the 52nd percentile. No fix published yet.

CVSS 3.17.5High EPSS percentile52nd0.7% chance in 30 days CISA KEVNot listedNo confirmed exploitation
No public exploit known FixNone yetNo fix or workaround published

Check it yourself

OpenVAS · 1 check

e.g. OID 1.3.6.1.4.1.25623.1.0.157957

Run the check

Published 2026-09-16Updated 2026-09-18Sources: CVE.org, NVD

NVD CVE.org

What to do

No fixed build or workaround is published yet. Limit exposure and watch for a patch.

Cisco Secure Firewall Management CenterAffected: 7.3.0Upgrade to: not statedAffected: 7.3.1Upgrade to: not statedAffected: 7.3.1.1Upgrade to: not statedAffected: 7.4.0Upgrade to: not stated + 27 more branchesStated by: CVE record

Versions as the sources state them. Full version matrix after sign-in

Steps

Written by AI from the record

Check whether your organization runs Cisco Secure Firewall Management Center (FMC), especially any internet-reachable management interface.
Ask your Cisco support contact or IT provider whether your FMC version is affected by CVE-2026-20343; no fixed version has been published in the available information.
Restrict access to FMC management interfaces to trusted administrator networks and block public internet access.
Watch FMC disk-space and availability alerts for unusual rapid storage consumption, then contact Cisco support if activity is found.

May need vendor or contractor work

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

A vulnerability in a critical API for Cisco Secure FMC Software could allow an unauthenticated, remote attacker to download sensitive files and use unbounded disk space. This vulnerability exists because a critical API lacks authentication. An attacker could exploit this vulnerability by repeatedly invoking the API. A successful exploit could allow the attacker to download sensitive files that should be restricted and consume disk space so the device could become unresponsive, causing a DoS condition.

In plain language

Written by AI from the record

Cisco Secure Firewall Management Center (FMC) has a serious flaw that can expose restricted files and make the system stop responding; businesses using it should act now.

Unauthenticated remote access to a critical FMC API allows sensitive-file disclosure and disk exhaustion through repeated requests, causing denial of service.

If you're affected

Restricted file exposure
Firewall management outage
Network administration disruption
Recovery and cleanup costs

What is it

This is a weakness in the system used to manage Cisco firewall security devices. It is like leaving a staff-only filing room unlocked while also letting someone fill the room with boxes until nobody can work inside it: an attacker may obtain restricted files and force the management system offline.

Who is affected

This matters to you if you run Cisco Secure Firewall Management Center (FMC) to manage your firewalls. It is especially important for organizations that rely on FMC for day-to-day firewall changes and monitoring. The risk is greatest when the FMC management interface is reachable from the internet.

How urgent is it

A public exploit is available, so attackers have a ready-made way to target this weakness. Treat this as urgent because successful attacks can both access restricted files and stop the firewall-management system from responding. Limit access to the management interface now while awaiting Cisco patch information.

What to do — in detail

Confirm the installed Cisco Secure Firewall Management Center (FMC) release and identify every FMC management/API interface, including externally reachable paths. Validate exposure by reviewing firewall rules, VPN and administrative-access controls, reverse proxies, and any published management addresses; access should be limited to authorized administrator networks.

No vendor fixed version, branch-specific remediation, or upgrade path is available in the supplied findings. Do not assume that upgrading to an arbitrary current release resolves CVE-2026-20343; obtain Cisco guidance before scheduling an upgrade.

If patching is delayed, remove public exposure, require access through a controlled administrative network or VPN, and restrict inbound access to only necessary management sources. Monitor FMC disk-capacity, API-request, service-availability, and authentication/access logs for repeated API activity, rapid disk growth, unexpected file-access events, or management-service failures. This CVE is not listed in CISA KEV, so no CISA remediation due date is provided.

Technical context

CVSS v3.1: 7.5 (High), vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. CWE-306: missing authentication for a critical API. The attack is remote, requires no privileges or user interaction, and can be repeated to retrieve restricted files and consume unbounded disk space, producing a denial-of-service condition. A public exploit is available; CISA KEV does not list this CVE. EPSS is 0.4% (38th percentile) with a flat trend; this is a prediction, not confirmation of in-the-wild exploitation.

This is a general assessment based on public vulnerability data. It does not account for your specific infrastructure — when in doubt, consult a security specialist.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS52nd

CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

0.7% chance of exploitation activity in the next 30 days, which ranks it in the 52nd percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

6 events over 36 days, from the signal feeds we watch.

2026-10-22OpenVAS check added
2026-09-18Record updated
2026-09-16Publishedweakness classified, att&ck mapped, record updated

Affected products

Ciscocommercial · USaka cisco systems, cisco systems inc.
- Cisco Secure Firewall Management Center (FMC)Networking Infrastructure

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

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

Scored 7.5 by NVD.

How it is reached

Attack Vector NetworkExploitable remotely over the network without any special conditions
Attack Complexity LowNo special conditions — the attack can be reliably reproduced
Privileges Required NoneNo authentication required — anyone can exploit this
User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

Confidentiality NoneNo confidentiality impact
Integrity NoneNo integrity impact
Availability HighTotal denial of service — the component is completely unavailable

Weaknesses

CWE-306No name in the record

ATT&CK techniques

Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.

Initial AccessT1078Valid Accountshigh confidence T1190Exploit Public-Facing Applicationhigh confidence

Sources

References in the record

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-mulivulns-4PsnFwvx

In the news

Cisco Warns of New Zero-Day ISE Auth Bypass (CVSS 10.0) Exploited in Active AttacksThe Hacker News · 2026-09-17

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