CVE-2026-40622 Another 'ghost domain names' attack variant

Medium 6.6 Published 20 May 2026 Updated 20 May 2026

Attackers can extend the ghost domain window by overwriting cached NS records, bypassing DNS security controls in Unbound.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-40622?

CVE-2026-40622 is a medium-severity vulnerability in Nlnetlabs Unbound, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-346

Which versions are affected by CVE-2026-40622?

It affects 1 product.

Products include Nlnetlabs Unbound.

How do I fix CVE-2026-40622?

Upgrade to a fixed version.

Is CVE-2026-40622 being exploited?

There is no known exploitation of CVE-2026-40622 in the wild and no public exploit code.

All Nlnetlabs Unbound vulnerabilities

Sources

Also known as ALPINE-CVE-2026-40622, AZL-87035, CLSA-2026-1780319730, CLSA-2026-1780479714, DEBIAN-CVE-2026-40622, ECHO-627e-e177-a81b and 3 more.