CVE-2026-35501 Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-35501?
CVE-2026-35501 is a low-severity vulnerability in NLnet Labs Unbound, published on 21 Oct 2026.
Official description
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.
Weakness: CWE-354
Which versions are affected by CVE-2026-35501?
How do I fix CVE-2026-35501?
Upgrade to a fixed version.
Is CVE-2026-35501 being exploited?
There is no known exploitation of CVE-2026-35501 in the wild and no public exploit code.
Sources
Also known as AZL-109821, DEBIAN-CVE-2026-35501, ECHO-bc3c-40d7-60f2, GHSA-mh74-9w87-h7vx, UBUNTU-CVE-2026-35501.