Description
In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads.
Published: 2026-09-16
Score: 4.4 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
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Remediation

Vendor Solution

This issue is fixed starting with version 1.26.1

Tracking

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History

Wed, 16 Sep 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

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


Wed, 16 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-367
References
Metrics threat_severity

None

threat_severity

Moderate


Wed, 16 Sep 2026 08:45:00 +0000

Type Values Removed Values Added
Description In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads.
Title Possible ZONEMD verification bypass window
Weaknesses CWE-345
References
Metrics cvssV3_1

{'score': 4.4, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: NLnet Labs

Published:

Updated: 2026-09-16T14:33:24.961Z

Reserved: 2026-09-07T14:06:21.947Z

Link: CVE-2026-77955

cve-icon Vulnrichment

Updated: 2026-09-16T14:33:22.241Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-09-16T09:17:05.780

Modified: 2026-09-16T19:41:10.423

Link: CVE-2026-77955

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-16T08:29:39Z

Links: CVE-2026-77955 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-16T14:15:09Z

Weaknesses