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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-35501)

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by multiple vulnerabilities as referenced in the 0be28489-cd2f-11f1-8135-8447094a420f advisory.

    NLNetLabs reports:
    This release consolidates security fixes for issues reported over     a period of time.

Tenable has extracted the preceding description block directly from the FreeBSD security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-35501)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
477080	Echo: unbound: security update to 1.26.2	Tenable Cloud Security	Echo Local Security Checks	Local	low
477080	Echo: unbound: security update to 1.26.2	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	low
370456	FreeBSD : Unbound -- Multiple vulnerabilities (0be28489-cd2f-11f1-8135-8447094a420f)	Nessus	FreeBSD Local Security Checks	Local	medium
370046	Linux Distros Unpatched Vulnerability : CVE-2026-35501	Nessus	Misc.	Local	low

Detections

Analytics

CVE-2026-35501

low

Tenable Plugins

low

low

medium

low