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.

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8282-1 Unbound vulnerabilities
Fixes

Solution

This issue is fixed starting with version 1.25.1


Workaround

No workaround given by the vendor.

History

Thu, 21 May 2026 08:30:00 +0000

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs unbound
Vendors & Products Nlnetlabs
Nlnetlabs unbound

Wed, 20 May 2026 16:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-107

Wed, 20 May 2026 13:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-346
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


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: 2026-05-20T12:12:33.115Z

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

Link: CVE-2026-40622

cve-icon Vulnrichment

Updated: 2026-05-20T12:12:21.123Z

cve-icon NVD

Status : Awaiting Analysis

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

Modified: 2026-05-20T14:02:12.280

Link: CVE-2026-40622

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-21T08:15:06Z

Weaknesses