Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.

When NLnet Labs Unbound 1.0.1 up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor with a forged NSEC reply with the SOA bit cleared can trick Unbound to treat the configured trust island as insecure. This happens because the DNSSEC validator in Unbound accepts and caches the NSEC insecure response bypassing the RRSIG validation that the validator was supposed to do. The acceptance of the NSEC record at the trust anchor apex was allowed due to and old fix for type DS and NSEC queries from clients when trust anchor for that name existed.

Source published

21 Oct 2026 08:56:55 UTC

Source modified

29 Oct 2026 19:05:26 UTC

Observed here

29 Oct 2026 21:14:49 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N