---
id: CVE-2026-35501
title: >-
  Bypass of a configured island trust anchor underneath an insecure parent from
  an atacker-controlled NSEC record.
summary: >-
  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 malic…
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-354
vendor: NLnet Labs
product: Unbound
affected:
  - Unbound >= 1.0.1 < 1.26.2
published: '2026-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T08:56:55.811Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-35501'
references:
  - url: 'https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-35501.txt'
tags:
  - cve.org
ingestedAt: '2026-10-21T09:46:15.397Z'
---

## Overview

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.

## Affected

- `Unbound >= 1.0.1 < 1.26.2`

## Remediation

This issue is fixed starting with version 1.26.2