CVE-2021-0267
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 · uneditedAn Improper Input Validation vulnerability in the active-lease query portion in JDHCPD's DHCP Relay Agent of Juniper Networks Junos OS allows an attacker to cause a Denial of Service (DoS) by sending a crafted DHCP packet to the device thereby crashing the jdhcpd DHCP service. This is typically configured for Broadband Subscriber Sessions. Continued receipt and processing of this crafted packet will create a sustained Denial of Service (DoS) condition. This issue affects Juniper Networks Junos OS: 19.4 versions prior to 19.4R3-S1; 20.1 versions prior to 20.1R2-S1, 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R2. This issue does not affect Junos OS Evolved.
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 confidenceImproper input validation in the active-lease query portion of JDHCPD's DHCP Relay Agent allows remote attackers to cause denial of service by sending crafted DHCP packets. The malformed packets crash the jdhcpd service, and continued receipt creates a sustained DoS condition.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 19.4= 20.1= 20.2= 20.3CVSS 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
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:A/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 Junos OS versionRun 'show version' or check system banner to confirm the installed Junos versionAffected if Version is 19.4, 20.1, 20.2, or 20.3 (any build variant of these releases)
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Confirm jdhcpd service is enabledRun 'show system processes extensive | match jdhcpd' or check if the DHCP relay daemon is active on the deviceAffected if The jdhcpd process is running and the DHCP Relay Agent feature is configured
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Verify DHCP Relay configurationRun 'show configuration | display set | match relay' or check for 'forwarding-options helpers' or 'relay' configuration under the logical systemAffected if DHCP relay is configured and active on any interface
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Check for jdhcpd crash historyRun 'show system core-dumps' or 'show log messages' for recent jdhcpd crash events, particularly around times of unexpected DHCP trafficAffected if Recent crashes of jdhcpd are logged without an obvious cause
The environment is affected if the device runs Junos 19.4, 20.1, 20.2, or 20.3 AND has the DHCP Relay Agent (jdhcpd) enabled and processing DHCP 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 dataUpgrade Junos OS to the fixed versions (19.4R3-S1, 20.1R2-S1/20.1R3, 20.2R3, or 20.3R2). Consider implementing traffic filtering or ACLs on upstream interfaces to reject malformed DHCP packets as an interim measure.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-0267 — 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-2021-0267 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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