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RecursorApplication · Powerdns

CVE-2026-33259

MEDIUM · 5.0 CVSS v3.1 Published 2026-04-22
Fix available
A fix is available. Upgrade to 5.2.9 / 5.3.6 or later.
See remediation →
56/100
Remediation priority · Elevated
Remotely reachable Zero-click

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 · unedited
Having many concurrent transfers of the same RPZ can lead to inconsistent RPZ data, use after free and/or a crash of the recursor. Normally concurrent transfers of the same RPZ zone can only occur with a malfunctioning RPZ provider.

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 confidence

This is a concurrency vulnerability in the PowerDNS Recursor's RPZ (Response Policy Zone) transfer handling. When a malfunctioning RPZ provider triggers many concurrent transfers of the same RPZ zone, race conditions can occur during zone transfer processing, leading to inconsistent RPZ data, use-after-free memory corruption, and potential recursor crashes.

MitigationEnsure the RPZ provider is functioning correctly and not generating spurious concurrent transfer requests; also upgrade to a patched version of PowerDNS Recursor when available.

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
RecursorApplication
Affected:>= 5.2.0, < 5.2.9>= 5.3.0, < 5.3.6= 5.4.0

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
High
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check PowerDNS Recursor version
    Run 'rec_control version' or 'pdns_recursor --version' to obtain the installed version number
    Affected if The version falls within >= 5.2.0 and < 5.2.9, >= 5.3.0 and < 5.3.6, or equals 5.4.0
  2. Verify RPZ is configured
    Inspect the recursor configuration for any 'rpz' or 'response-policy-zone' settings. Common locations include the main config file or included configuration directories
    Affected if One or more RPZ zones are configured and loaded by the recursor
  3. Identify RPZ providers
    Review the RPZ configuration to determine which providers are in use. Look for primary/secondary addresses or URLs configured for each RPZ zone
    Affected if External RPZ providers are configured, especially if they are third-party or internet-facing
  4. Check for crash logs or instability
    Examine recursor logs and system logs (such as journalctl for pdns-recursor) for recent crashes, use-after-free errors, or assertions related to RPZ processing
    Affected if Recent crashes or error messages mention RPZ transfer handling, memory corruption, or race conditions
  5. Review transfer activity
    Check logs for patterns of excessive or anomalous RPZ zone transfer requests occurring in short time periods
    Affected if Logs show many concurrent or overlapping transfer attempts for the same RPZ zone

A user is affected if PowerDNS Recursor is running an unpatched version (5.2.0-5.2.8, 5.3.0-5.3.5, or 5.4.0) with RPZ configured and a malfunctioning provider is triggering concurrent transfers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Upgrade available Upgrade to 5.2.9 / 5.3.6 or later
Fixed in 5.2.95.3.6
Interim mitigation

Ensure the RPZ provider is functioning correctly and not generating spurious concurrent transfer requests; also upgrade to a patched version of PowerDNS Recursor when available.

Recommended fix High confidence

Upgrade to Recursor 5.2.9, 5.3.6, or 5.4.1 (latest stable release)

  1. 1. Identify the current PowerDNS Recursor version by running 'rec_control version' or checking your package manager
  2. 2. Stop the PowerDNS Recursor service (e.g., 'systemctl stop pdns-recursor' or 'service pdns-recursor stop')
  3. 3. Backup your Recursor configuration files (typically in /etc/pdns-recursor/) and any custom RPZ configurations
  4. 4. Upgrade the PowerDNS Recursor package to version 5.2.9, 5.3.6, or 5.4.1 depending on your current major version branch
  5. 5. Verify the installed version matches the expected fixed release
  6. 6. Review and restore any custom configuration if needed
  7. 7. Start the PowerDNS Recursor service (e.g., 'systemctl start pdns-recursor' or 'service pdns-recursor start')
  8. 8. Monitor logs for any errors and verify normal operation
Caveat Minor version upgrades typically maintain backward compatibility; review release notes for any configuration changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Recursor Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,210
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-33259 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data