dbcve.org
UnboundApplication · Nlnetlabs

CVE-2026-42944

HIGH · 7.5 CVSS v3.1 Published 2026-05-20
Fix available
A fix is available. Upgrade to 1.25.1 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
NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

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 heap overflow vulnerability in the EDNS option encoding logic. When multiple NSID, DNS Cookie, or EDNS Padding options are present in a query, a flaw in the size calculation truncates the EDNS field size, causing the encoder to write beyond allocated buffer space. This results in heap overflow of Unbound-controlled data, leading to potential crash.

MitigationUpgrade to Unbound 1.25.1 or later, which contains fixes for EDNS option de-duplication and size calculation. If immediate patching is not feasible, disable the 'nsid', 'answer-cookie', and 'pad-responses' options until the update can be applied.

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
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. Check if Unbound is installed and its version
    Run `unbound -V` or `unbound-checkconf -v` to obtain the installed version number
    Affected if The installed version is between 1.14.0 and 1.25.0 inclusive (versions 1.14.0 <= version < 1.25.1)
  2. Identify if NSID option is enabled
    Search the Unbound configuration file (commonly /etc/unbound/unbound.conf or /etc/unbound.conf) for the `nsid` directive
    Affected if The `nsid` option is present and enabled in the configuration
  3. Identify if DNS Cookie option is enabled
    Search the Unbound configuration file for the `answer-cookie` directive
    Affected if The `answer-cookie` option is present and enabled in the configuration
  4. Identify if EDNS Padding option is enabled
    Search the Unbound configuration file for the `pad-responses` directive
    Affected if The `pad-responses` option is present and enabled in the configuration

The environment is affected if Unbound version is 1.14.0 through 1.25.0 AND at least one of the options (nsid, answer-cookie, or pad-responses) is enabled in the Unbound configuration.

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 to Unbound 1.25.1 or later, which contains fixes for EDNS option de-duplication and size calculation. If immediate patching is not feasible, disable the 'nsid', 'answer-cookie', and 'pad-responses' options until the update can be applied.

Recommended fix High confidence

Unbound 1.25.1

  1. Identify the current Unbound version installed using 'unbound -V' or checking the package manager
  2. Upgrade Unbound to version 1.25.1 or later from the official NLnet Labs repository or your distribution's package manager
  3. After upgrading, verify the new version is running with 'unbound -V'
  4. If using 'nsid', 'answer-cookie', or 'pad-responses' options, confirm they are functioning correctly after the upgrade
  5. Restart the Unbound service to ensure the new version is loaded

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

Fix this in Unbound Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,512.

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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-2026-42944 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