NLnet Labs Unbound 1.16.2 up to and including version 1.25.0 has a vulnerability of the 'ghost domain names' family of attacks that could extend the ghost domain window by up to one cached TTL configured value. Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be able to query a vulnerable Unbound. A single client NS query can cause Unbound to overwrite the cached expired parent-side referral NS rrset with the child-side apex NS rrset and essentially extend the ghost domain window by up to one cached TTL configured value ('cache-max-ttl'). In configurations where 'harden-referral-path: yes' is used (non-default configuration), no client NS query is required since Unbound implicitly performs that query. Unbound 1.25.1 contains a patch with a fix that does not allow extension of TTLs for (parent) NS records regardless of their trust.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
NLnet Labs Unbound unaffected
Version Status Constraints
1.16.2 affected < 1.25.1

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Project Subscriptions

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Advisories

No advisories yet.

Fixes

Solution

This issue is fixed starting with version 1.25.1

Workaround

No workaround given by the vendor.

References
Link Providers
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40622.txt cve-icon cve-icon
History

Wed, 20 May 2026 11:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-107

Wed, 20 May 2026 10:00:00 +0000

Type Values Removed Values Added
Description NLnet Labs Unbound 1.16.2 up to and including version 1.25.0 has a vulnerability of the 'ghost domain names' family of attacks that could extend the ghost domain window by up to one cached TTL configured value. Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be able to query a vulnerable Unbound. A single client NS query can cause Unbound to overwrite the cached expired parent-side referral NS rrset with the child-side apex NS rrset and essentially extend the ghost domain window by up to one cached TTL configured value ('cache-max-ttl'). In configurations where 'harden-referral-path: yes' is used (non-default configuration), no client NS query is required since Unbound implicitly performs that query. Unbound 1.25.1 contains a patch with a fix that does not allow extension of TTLs for (parent) NS records regardless of their trust.
Title Another 'ghost domain names' attack variant
References
Metrics cvssV4_0

{'score': 6.6, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: NLnet Labs

Published:

Updated: 2026-05-20T09:18:41.816Z

Reserved: 2026-05-07T10:07:51.817Z

Link: CVE-2026-40622

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-05-20T10:16:26.850

Modified: 2026-05-20T10:16:26.850

Link: CVE-2026-40622

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-20T11:30:26Z

Weaknesses