Description
In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.
Published: 2026-09-16
Score: 7.5 High
EPSS: n/a
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

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History

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

Type Values Removed Values Added
Description In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.
Title Possible heap buffer overflow during DNSSEC canonicalization
Weaknesses CWE-122
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

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cve-icon MITRE

Status: PUBLISHED

Assigner: NLnet Labs

Published:

Updated: 2026-09-16T08:30:15.428Z

Reserved: 2026-09-07T14:06:21.967Z

Link: CVE-2026-81634

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-16T09:17:06.210

Modified: 2026-09-16T09:17:06.210

Link: CVE-2026-81634

cve-icon Redhat

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cve-icon OpenCVE Enrichment

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Weaknesses