CVE-2026-50106

Possible insecure NXDOMAIN for non-existing records under a configured island trust anchor underneath an insecure parent.

Published Oct 21, 2026 CVSS 3.1 · 6.5 Medium EPSS < 1% KEV · Not listed
Description
When NLnet Labs Unbound 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 who can deliver one forged NXDOMAIN response for a name inside the island, with the NSEC/SOA RRSIG 'SignerName' set to the insecure parent, tricks Unbound's validator to use the root trust anchor instead, and consecutively the insecure parent, thus causing that record to be treated as insecure and denying existence for records in the trust island.

Remediation

Vendor Solution

This issue is fixed starting with version 1.26.2

Tracking

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Advisories

Source ID Title
Debian DSA Debian DSA DSA-6581-1 unbound security update
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs unbound
Vendors & Products Nlnetlabs
Nlnetlabs unbound
Type Values Removed Values Added
Description When NLnet Labs Unbound 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 who can deliver one forged NXDOMAIN response for a name inside the island, with the NSEC/SOA RRSIG 'SignerName' set to the insecure parent, tricks Unbound's validator to use the root trust anchor instead, and consecutively the insecure parent, thus causing that record to be treated as insecure and denying existence for records in the trust island.
Title Possible insecure NXDOMAIN for non-existing records under a configured island trust anchor underneath an insecure parent.
Weaknesses CWE-807
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
NLnet Labs
Published
Updated
Oct 29, 2026, 7:06 PM
Reserved
Jun 22, 2026, 10:11 AM
Status
Awaiting Analysis
Published
Oct 21, 2026, 9:17 AM
Modified
Oct 29, 2026, 7:17 PM