dbcve.org
UnboundApplication · Nlnetlabs

CVE-2026-44608

MEDIUM · 5.9 CVSS v3.1 Published 2026-05-20
Fix available
A fix is available. Upgrade to 1.25.1 or later.
See remediation →
68/100
Remediation priority · Elevated
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
NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

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 confidence

Unbound 1.14.0-1.25.0 contains a locking inconsistency during RPZ (Response Policy Zone) XFR (zone transfer) reloads in multi-threaded environments. When an RPZ zone with 'rpz-nsip' or 'rpz-nsdname' triggers experiences an XFR simultaneously with another thread reading that zone, the reader may not hold the lock long enough, causing the applying thread to free objects the reader is about to access, resulting in heap use-after-free and crash.

MitigationUpgrade Unbound to version 1.25.1 or later. Alternatively, disable RPZ XFR transfers or avoid using 'rpz-nsip'/'rpz-nsdname' triggers if upgrade is not immediately feasible.

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
UnboundApplication
Affected:>= 1.14.0, < 1.25.1

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 checks

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

  1. Check Unbound version
    Run 'unbound -V' or 'unbound-control version' to determine the installed version
    Affected if Version is >= 1.14.0 and < 1.25.1
  2. Verify multi-threaded operation
    Check unbound.conf for 'num-threads:' setting greater than 1, or check command line for multiple worker processes
    Affected if Unbound is running with more than one thread or worker process
  3. Confirm RPZ is enabled
    Search unbound.conf for 'rpz:' configuration blocks or 'response-policy:' directives
    Affected if RPZ (Response Policy Zones) is configured and active
  4. Check for RPZ zone transfer (XFR) configuration
    Look in unbound.conf for 'zone:' entries with 'allow-xfr:' or 'request-xfr:' directives pointing to master/slave servers
    Affected if RPZ zone transfers (XFR) are configured, meaning RPZ zones are being transferred from external sources
  5. Identify RPZ trigger types in use
    Inspect RPZ zone files or RPZ configuration for 'rpz-nsip' or 'rpz-nsdname' policy actions
    Affected if RPZ zones contain 'rpz-nsip' or 'rpz-nsdname' trigger types

All conditions must be present: running a vulnerable Unbound version (1.14.0-1.25.0) in multi-threaded mode with RPZ enabled, RPZ XFR configured, and rpz-nsip or rpz-nsdname triggers in use.

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 1.25.1 or later
Fixed in 1.25.1
Interim mitigation

Upgrade Unbound to version 1.25.1 or later. Alternatively, disable RPZ XFR transfers or avoid using 'rpz-nsip'/'rpz-nsdname' triggers if upgrade is not immediately feasible.

Recommended fix High confidence

Unbound 1.25.1

  1. Check current Unbound version using 'unbound -V' or 'unbound-control version'
  2. Stop the Unbound service using 'systemctl stop unbound' or the appropriate command for your system
  3. Upgrade Unbound to version 1.25.1 or later using your system's package manager (e.g., 'apt-get update && apt-get install unbound' or 'yum update unbound')
  4. Start the Unbound service using 'systemctl start unbound'
  5. Verify the upgrade was successful by running 'unbound -V' to confirm version 1.25.1 or later is installed
  6. If using RPZ with multi-threading, verify configuration to ensure RPZ XFR reload behavior is as expected after upgrade
Caveat No major breaking changes expected; this is a bugfix release addressing a race condition

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

Fix this in Unbound Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,280
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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-2026-44608 in production — separate from our analysis above.

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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
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  • Version or environment caveats, and links to real fixes
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