CVE-2025-40779
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 · uneditedIf a DHCPv4 client sends a request with some specific options, and Kea fails to find an appropriate subnet for the client, the `kea-dhcp4` process will abort with an assertion failure. This happens only if the client request is unicast directly to Kea; broadcast messages do not cause the problem. This issue affects Kea versions 2.7.1 through 2.7.9, 3.0.0, and 3.1.0.
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 ISC Kea's DHCPv4 server. When a DHCPv4 client sends a unicast request containing specific options that cannot be matched to any configured subnet, the kea-dhcp4 process aborts due to an assertion failure. Broadcast requests do not trigger this issue. The vulnerability affects versions 2.7.1-2.7.9, 3.0.0, and 3.1.0.
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
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 installed Kea DHCP versionRun 'kea-dhcp4 -v' or check your package manager (dpkg -r kea-dhcp4, rpm -qi kea-dhcp4) to find the exact version numberAffected if The version is 2.7.1 through 2.7.9, 3.0.0, or 3.1.0
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Confirm kea-dhcp4 service is activeRun 'systemctl status kea-dhcp4' or 'ps aux | grep kea-dhcp4' to verify the DHCPv4 server process is runningAffected if The kea-dhcp4 process is running on the affected version
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Inspect Kea configuration for unicast supportExamine your Kea configuration file (typically /etc/kea/kea-dhcp4.conf) and look for 'unicast' settings in interface-config or dhcp-server-identifier options that enable unicast responsesAffected if Unicast is enabled in the configuration and the server accepts unicast DHCPv4 requests
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Review subnet configuration completenessCheck your Kea dhcp4/subnet4 configuration section and verify that all expected client subnets are defined. Look for any address pools that might have no matching subnetAffected if There are configured subnets but clients on certain network segments might send requests with options that do not match any defined subnet
You are affected if running a vulnerable Kea version (2.7.1-2.7.9, 3.0.0, or 3.1.0) with the DHCPv4 server active and unicast requests can reach it from clients that may not match any configured subnet.
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 dataUpgrade to a patched version of Kea once available. As a workaround, ensure all expected client requests can be matched to configured subnets, or restrict unicast access to trusted clients only.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-40779 — 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-2025-40779 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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- Version or environment caveats, and links to real fixes
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