CVE-2020-12667
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 · uneditedKnot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an attacker-controlled server, aka an "NXNSAttack" issue. This is triggered by random subdomains in the NSDNAME in NS records.
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 confidenceKnot Resolver before 5.1.1 suffers from the NXNSAttack vulnerability where an attacker-controlled DNS server sends crafted DNS responses containing random subdomains in NSDNAME fields of NS records. When the resolver processes these responses, it attempts to resolve all the random subdomains, creating significant traffic amplification that can be used for DDoS attacks against the resolver or downstream targets.
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< 5.1.1CVSS 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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Verify Knot Resolver is installedRun 'kresd --version' or check your package manager for the knot-resolver package (e.g., 'dpkg -l | grep knot-resolver' on Debian/Ubuntu, 'rpm -qa | grep knot-resolver' on RHEL/CentOS)Affected if Knot Resolver is present on the system
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Determine installed versionExecute 'kresd --version' to display the version number, or use your package manager query command from the previous step to show the installed versionAffected if The version shown is lower than 5.1.1 (e.g., 5.1.0, 5.0.x, 4.x.x)
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Confirm daemon is running and processing DNS queriesCheck if the kresd process is active (e.g., 'systemctl status kresd' or 'ps aux | grep kresd') and review DNS query logs if availableAffected if The resolver is actively handling DNS queries and is version 5.1.1 or lower
If Knot Resolver is installed and the running version is lower than 5.1.1, the environment is vulnerable to the NXNSAttack amplification vector.
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 data5.1.1
Upgrade Knot Resolver to version 5.1.1 or later to patch the vulnerability. Additionally, consider implementing rate limiting on DNS queries and filtering responses from untrusted DNS servers.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2020-12667 — 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-2020-12667 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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