CVE-2025-20133
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedA vulnerability in the management and VPN web servers of the Remote Access SSL VPN feature of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an unauthenticated, remote attacker to cause the device to unexpectedly stop responding, resulting in a DoS condition. This vulnerability is due to ineffective validation of user-supplied input during the Remote Access SSL VPN authentication process. An attacker could exploit this vulnerability by sending a crafted request to the VPN service on an affected device. A successful exploit could allow the attacker to cause a DoS condition where the device stops responding to Remote Access SSL VPN authentication requests.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThis is a denial-of-service vulnerability in Cisco ASA and FTD appliances affecting the Remote Access SSL VPN feature. The issue stems from insufficient input validation during the VPN authentication process, allowing an unauthenticated remote attacker to send specially crafted requests that cause the device to stop responding to VPN authentication.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify the device modelRun 'show version' or check the device CLI output to confirm the device is Cisco ASA or Cisco Firepower Threat Defense (FTD)Affected if The device is not an ASA or FTD appliance
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Check if SSL VPN is enabledRun 'show vpn-sessiondb' or 'show run | include ssl' in the device CLI to see if any Remote Access SSL VPN configurations existAffected if No SSL VPN remote access tunnels are configured or enabled
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Verify the software versionRun 'show version' and locate the firmware/software version string. Compare this against Cisco's official affected version list for CVE-2025-20133Affected if The installed version is not within the Cisco-published affected version range
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Confirm VPN interface accessibilityCheck if the outside/SSL VPN interface is reachable from untrusted networks by reviewing the interface configuration with 'show interface ip brief'Affected if SSL VPN interfaces are isolated to trusted networks only
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Look for service degradation symptomsMonitor VPN authentication responsiveness. Use 'show vpn-sessiondb summary' to check for authentication failures or unresponsive states after unusual request patternsAffected if VPN authentication continues functioning normally without unexpected failures
A user is affected if they run a vulnerable Cisco ASA or FTD appliance with Remote Access SSL VPN enabled, the software version falls within the vendor-affected range, and the VPN interface is externally accessible.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply the vendor-supplied software update when available. As an interim measure, consider implementing rate limiting on VPN interfaces and restricting VPN access to known, trusted IP ranges if feasible.
- Consultation2.0 h
- Implementation3.0 h
- Testing3.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-20133 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-20133 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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