CVE-2024-20266
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 DHCP version 4 (DHCPv4) server feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to trigger a crash of the dhcpd process, resulting in a denial of service (DoS) condition. This vulnerability exists because certain DHCPv4 messages are improperly validated when they are processed by an affected device. An attacker could exploit this vulnerability by sending a malformed DHCPv4 message to an affected device. A successful exploit could allow the attacker to cause a crash of the dhcpd process. While the dhcpd process is restarting, which may take approximately two minutes, DHCPv4 server services are unavailable on the affected device. This could temporarily prevent network access to clients that join the network during that time period and rely on the DHCPv4 server of the affected device. Notes: Only the dhcpd process crashes and eventually restarts automatically. The router does not reload. This vulnerability only applies to DHCPv4. DHCP version 6 (DHCPv6) is not affected.
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 vulnerability in Cisco IOS XR Software's DHCPv4 server allows an unauthenticated remote attacker to crash the dhcpd process by sending malformed DHCPv4 messages. The improper validation of DHCPv4 messages during processing leads to a denial of service, with the process automatically restarting after approximately two minutes.
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
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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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Confirm Cisco IOS XR Software is in useRun 'show version' or 'uname -a' on the device to verify the operating system is Cisco IOS XR.Affected if The device is running Cisco IOS XR Software (any version).
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Verify DHCPv4 server is enabledExecute 'show running-config | include dhcp' or check the configuration for 'ipv4 dhcp server' or 'dhcpv4 server' service entries.Affected if DHCPv4 server feature is configured and active on the device.
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Check the IOS XR version against affected releasesRun 'show version' and compare the displayed IOS XR release number against the Cisco Security Advisory for CVE-2024-20266 listing the specific affected version ranges.Affected if The installed IOS XR version falls within the affected version range published by Cisco for this CVE.
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Assess network exposure to DHCPv4 trafficReview interface configurations and ACLs to determine if the device DHCPv4 server is reachable from untrusted or external networks.Affected if DHCPv4 server is accessible from untrusted network segments or the internet without filtering.
The environment is affected if the device runs Cisco IOS XR with a version in the affected range and has the DHCPv4 server enabled and exposed to untrusted DHCPv4 traffic.
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 Cisco vendor patch for this vulnerability. As an interim measure, implement network segmentation or ACLs to restrict DHCPv4 traffic to trusted sources only.
- Consultation4.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2024-20266 — 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-2024-20266 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
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- Version or environment caveats, and links to real fixes
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