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RecursorApplication · Powerdns

CVE-2026-33256

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
An attacker can send a web request that causes unlimited memory allocation in the internal web server, leading to a denial of service. The internal web server is disabled by default.

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

The internal web server has a memory allocation vulnerability where certain web requests trigger unlimited/unbounded memory consumption, causing the server to exhaust available memory and become unavailable. This is a denial-of-service vulnerability exploitable via specially crafted HTTP requests.

MitigationIf the internal web server is not required in production, leave it disabled. If enabled, implement request size limits, timeout configurations, and memory consumption constraints at the application or infrastructure layer to prevent memory exhaustion from malformed requests.

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. Determine Powerdns Recursor installed version
    Run 'rec_control version' or check package manager (dpkg -l pdns-recursor, rpm -q pdns-recursor)
    Affected if Version falls in ranges >=5.2.0 <5.2.9, >=5.3.0 <5.3.6, or exactly 5.4.0
  2. Verify if internal web server is enabled
    Check configuration file (typically /etc/pdns-recursor/recursor.conf) for 'webserver=yes' or 'api=yes' directives
    Affected if The internal web server is set to enabled (webserver=yes)
  3. Confirm web server listen address
    Inspect 'webserver-address' and 'webserver-port' settings in recursor.conf to determine if the service is bound to accessible network interfaces
    Affected if Web server is bound to a routable IP address (0.0.0.0) rather than localhost only
  4. Check for web request size limits
    Look for 'webserver-max-bodiesize' or similar size-limiting directives in recursor.conf
    Affected if No explicit request size limit is configured, allowing potentially unbounded request handling

You are affected if Powerdns Recursor version is in the affected ranges AND the internal web server is enabled and accessible.

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

If the internal web server is not required in production, leave it disabled. If enabled, implement request size limits, timeout configurations, and memory consumption constraints at the application or infrastructure layer to prevent memory exhaustion from malformed requests.

Recommended fix High confidence

5.2.9, 5.3.6, or 5.4.1 (depending on your current version branch)

  1. 1. Identify the currently installed PowerDNS Recursor version using 'rec_control version' or checking the package management system
  2. 2. Based on your current version line, plan upgrade to the next stable release: For 5.2.x upgrade to 5.2.9+, for 5.3.x upgrade to 5.3.6+, for 5.4.0 upgrade to 5.4.1 or later
  3. 3. Before upgrading, review the release notes for your target version at docs.powerdns.com/recursor/changelog.html
  4. 4. Backup current configuration files (recursor.conf) and any custom settings
  5. 5. Upgrade the package using your system's package manager (apt-get, yum, or dnf depending on OS)
  6. 6. Restart the PowerDNS Recursor service to apply the update
  7. 7. Verify the new version is running with 'rec_control version'
  8. 8. Confirm the internal web server configuration if enabled - ensure it has appropriate resource limits if still needed
Caveat Review release notes for breaking changes between your current version and target version before upgrading

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

Fix this in Recursor Scoped from the published advisory
  • Consultation2.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,800
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,480.

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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-2026-33256 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