Vulnerability in Nlnet Labs Unbound
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.001 (2.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 3rd percentile — 2.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: 0.000
Affected products
- Nlnet Labs Unbound — versions 1.16.2
- Nlnetlabs Unbound
Weakness classification (CWE)
References
- www.nlnetlabs.nl/downloads/unbound/CVE-2026-40622.txt (vendor-advisory, Patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-40622?
- CVE-2026-40622 is a high-severity vulnerability in Nlnet Labs Unbound, classified under Origin Validation Error. CVSS score: 7.5/10. Published 2026-05-20.
- How severe is CVE-2026-40622?
- High severity. CVSS v3 base score is 7.5 out of 10.