CVE-2026-40622
Published: 20 May 2026
Summary
CVE-2026-40622 is a medium-severity Origin Validation Error (CWE-346) vulnerability in Nlnetlabs Unbound. Its CVSS base score is 6.6 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 6.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-31080
Vulnerability details
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vuln in public-facing DNS resolver (Unbound) directly enables remote exploitation (T1190); ghost domain NS record manipulation facilitates DNS C2/abuse (T1071.004).
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Requires unique identification of the service before communications, addressing failures to validate the origin of the interaction.
Trusted path establishment enforces validation that the communication originates from and reaches only the intended trusted system components.
Enforces validation of the true origin of DNS responses via signatures and chain-of-trust mechanisms.
Enforces origin validation of name/address data, eliminating reliance on unverified or impersonated DNS sources.
Mandates origin validation so that only legitimate endpoints can continue the authenticated session.