CVE-2026-42387
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 malicious authoritative server can send a crafted zone via the ZoneToCache function that leads to a crash of the Recursor due to insuffcient input validation.
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 · moderate confidenceA vulnerability in PowerDNS Recursor's ZoneToCache function allows a malicious authoritative server to send a specially crafted zone that causes the Recursor to crash due to insufficient input validation. An attacker controlling an authoritative server can exploit this by serving malformed zone data to vulnerable Recursor instances.
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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:H/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 PowerDNS Recursor is installedCheck for the presence of the pdns_recursor binary: which pdns_recursor or rpm -q pdns-recursorAffected if pdns_recursor is not found on the system
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Determine the installed Recursor versionRun pdns_recursor --version to obtain the version numberAffected if version is within the affected range (compare to patched versions when available)
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Check if ZoneToCache is configuredExamine the Recursor configuration file (typically /etc/pdns-recursor/recursor.conf) for zonetocache entries: grep -i zonetocache /etc/pdns-recursor/recursor.confAffected if ZoneToCache is enabled with at least one zone defined
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Identify authoritative servers allowed to provide zonesReview the configuration for zones supplied by remote servers: grep -E '(zoneToCache|xfr|slave)' /etc/pdns-recursor/recursor.confAffected if ZoneToCache pulls zones from servers that are not trusted or are externally accessible
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Verify access controls on zone provisionCheck for allow-from or xfr-axis statements in the configuration that restrict which servers can provide zones: grep -E 'allow-from|xfr' /etc/pdns-recursor/recursor.confAffected if No restrictive access controls exist, or the allowed sources include untrusted networks
A user is affected if PowerDNS Recursor is running with ZoneToCache enabled and pulling zones from authoritative servers that are not fully trusted or are exposed to potential malicious actors.
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 patched versions when available, and restrict which authoritative servers can provide zones to the Recursor through access controls.
- Consultation3.0 h
- Implementation8.0 h
- Testing5.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-42387 — 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-2026-42387 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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