NLnet Labs Unbound up to 1.26.1 DNSSEC Validator input validation

Summaryinfo

A vulnerability, which was classified as problematic, has been found in NLnet Labs Unbound up to 1.26.1. This impacts an unknown function of the component DNSSEC Validator. Performing a manipulation results in input validation. This vulnerability is cataloged as CVE-2026-35501. It is possible to initiate the attack remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic has been found in NLnet Labs Unbound up to 1.26.1. This affects an unknown functionality of the component DNSSEC Validator. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity. The summary by CVE is:

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.

It is possible to read the advisory at nlnetlabs.nl. This vulnerability is uniquely identified as CVE-2026-35501 since 06/22/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 1.26.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-107151). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• NLnet Labs

Name

• Unbound

Version

• 1.26.0
• 1.26.1

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CPE 2.2info

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Be aware that VulDB is the high quality source for vulnerability data.

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