dbcve.org
RecursorApplication · Powerdns

CVE-2026-33258

HIGH · 7.5 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 →
84/100
Remediation priority · High
Remotely reachable No privileges 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
By publishing and querying a crafted zone an attacker can cause allocation of large entries in the negative and aggressive NSEC(3) caches.

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 DNS cache exhaustion vulnerability where an attacker can publish a specially crafted DNS zone and query it to force the DNS resolver to allocate unusually large entries in negative caching and aggressive NSEC3 proof caches, potentially leading to memory exhaustion and denial of service.

MitigationImplement cache size limits and query rate limiting on DNS resolvers; apply vendor patches when available to restrict maximum cache entry sizes for negative and NSEC3 records.

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
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 checks

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

  1. Identify Powerdns Recursor version
    Run 'rec_control get-version' or check the installed package version with your package manager (e.g., 'dpkg -l pdns-recursor' or 'rpm -qi pdns-recursor')
    Affected if The installed version falls within any of these ranges: >= 5.2.0 and < 5.2.9; >= 5.3.0 and < 5.3.6; or exactly 5.4.0
  2. Confirm DNSSEC validation is enabled
    Check the recursor configuration file (typically /etc/powerdns/recursor.conf) for the 'dnssec' setting, or run 'rec_control get-dnssec'
    Affected if dnssec is set to 'validate' or 'log-failed' (the vulnerability exploits aggressive NSEC3 caching which only occurs when DNSSEC validation is active)
  3. Verify negative caching is permitted
    Check the recursor config for 'max-negative-ttl' or 'max-cache-entries' settings, or run 'rec_control get max-negative-ttl' if available
    Affected if Negative caching is enabled (default behavior) - the vulnerability exploits large entries in the negative cache
  4. Confirm the recursor is exposed to untrusted query sources
    Review the 'allow-from' or 'listen-address' settings in the recursor configuration to determine if queries from external sources are accepted
    Affected if The recursor accepts queries from networks beyond localhost, allowing an external attacker to publish a malicious zone and query it
  5. Check current cache usage and limits
    Run 'rec_control get-all' or 'rec_control get-cache-entries' to view current cache statistics, and review 'max-cache-entries' in the configuration
    Affected if Cache limits are unset or set very high (default is unlimited), meaning the resolver could allocate excessive memory to cache malicious entries

You are affected if running a vulnerable Powerdns Recursor version (5.2.0-5.2.8, 5.3.0-5.3.5, or 5.4.0) with DNSSEC validation enabled and the resolver accepts external queries.

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

Implement cache size limits and query rate limiting on DNS resolvers; apply vendor patches when available to restrict maximum cache entry sizes for negative and NSEC3 records.

Recommended fix High confidence

Upgrade to Recursor 5.2.9, 5.3.6, or 5.4.1+

  1. 1. Identify the currently running PowerDNS Recursor version using 'rec_control version' or 'pdns_recursor --version'
  2. 2. Stop the PowerDNS Recursor service
  3. 3. Update the package repository and upgrade the recursor package to version 5.2.9, 5.3.6, or 5.4.1 or later
  4. 4. Verify the new version is installed correctly
  5. 5. Start the PowerDNS Recursor service
  6. 6. Monitor system resources (memory, CPU) to confirm the resource allocation issue is resolved
Caveat Review PowerDNS Recursor release notes for any configuration or behavior changes between your current version and the target fixed version

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

Fix this in Recursor Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.

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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-2026-33258 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