CVE-2025-20239
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 Internet Key Exchange Version 2 (IKEv2) feature of Cisco IOS Software, IOS XE Software, Secure Firewall Adaptive Security Appliance (ASA) Software, and Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a memory leak, resulting in a denial of service (DoS) condition. This vulnerability is due to a lack of proper processing of IKEv2 packets. An attacker could exploit this vulnerability by sending crafted IKEv2 packets to an affected device. In the case of Cisco IOS and IOS XE Software, a successful exploit could allow the attacker to cause the device to reload unexpectedly. In the case of Cisco ASA and FTD Software, a successful exploit could allow the attacker to partially exhaust system memory, causing system instability such as being unable to establish new IKEv2 VPN sessions. A manual reboot of the device is required to recover from this condition.
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 confidenceA memory leak vulnerability in the IKEv2 feature of Cisco IOS, IOS XE, ASA, and FTD software allows an unauthenticated remote attacker to send crafted IKEv2 packets that trigger uncontrolled memory consumption. For IOS/IOS XE devices this causes unexpected reloads; for ASA/FTD devices it causes memory exhaustion preventing new IKEv2 VPN session establishment, requiring manual reboot to recover.
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 product and versionRun 'show version' on the device to determine if it is running Cisco IOS, IOS XE, ASA, or FTD and note the exact software version numberAffected if Device runs any of the affected product families (IOS, IOS XE, ASA, FTD) and version falls within the vulnerable range
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Verify IKEv2 is configuredRun 'show crypto ikev2 session' or check running configuration for 'crypto ikev2' commandsAffected if IKEv2 is enabled and configured on the device - the vulnerability only affects devices with active IKEv2 configurations
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Check device network exposureReview interface configurations and ACLs to determine if UDP port 500 (IKE) and UDP port 4500 (NAT-T) are accessible from untrusted/external networksAffected if IKEv2 interfaces are reachable from untrusted networks such as the internet - the attacker needs to send packets to these ports
A device is affected if it runs a vulnerable version of IOS, IOS XE, ASA, or FTD AND has IKEv2 enabled AND is exposed to untrusted networks on IKEv2 ports (UDP 500/4500).
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 Cisco security updates for affected software versions once released; consider IKEv2 rate limiting or ACL filtering at network edge as temporary mitigation to reduce attack surface.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-20239 — 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-2025-20239 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
- No weaponised exploit code, or anything meant to cause harm
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