CVE-2026-40622

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.