CVE-2026-40622

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40622.txt	Vendor Advisory Patch

Configurations

Configuration 1 (hide)

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*

History

26 May 2026, 18:28

Type	Values Removed	Values Added
First Time		Nlnetlabs Nlnetlabs unbound
References	~~() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40622.txt -~~	() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40622.txt - Vendor Advisory, Patch
CPE		cpe:2.3:a:nlnetlabs:unbound::::::::
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 7.5

20 May 2026, 13:16

Type	Values Removed	Values Added
CWE		CWE-346

20 May 2026, 10:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-05-20 10:16

Updated : 2026-05-26 18:28

NVD link : CVE-2026-40622

Mitre link : CVE-2026-40622

CVE.ORG link : CVE-2026-40622

JSON object : View

Products Affected

nlnetlabs

unbound

CWE

CWE-346

Origin Validation Error

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