Possible heap buffer overflow during DNSSEC canonicalization

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-81634
StatePUBLISHED
AssignerNLnet Labs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 09:17:06 UTC
Updated2026-09-23 19:51:14 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.004580000 probability, percentile 0.369590000 (date 2026-09-24)

Problem Types: CWE-122 | CWE-122 CWE-122: Heap-based Buffer Overflow

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNACVSS7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Nlnetlabs Unbound All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA NLnet Labs Unbound affected 1.26.1 semver Not specified

References

ReferenceSourceLinkTags
www.nlnetlabs.nl/downloads/unbound/CVE-2026-81634.txt [email protected] www.nlnetlabs.nl Patch, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Vlatko Kosturjak (Marlink Cyber) (en)

Additional Advisory Data

SourceTimeEvent
CNA2026-07-31T00:00:00.000ZIssue reported by Vlatko Kosturjak
CNA2026-08-03T00:00:00.000ZNLnet Labs shares patch
CNA2026-08-04T00:00:00.000ZVlatko Kosturjak verifies patch
CNA2026-09-16T00:00:00.000ZFixes released with version 1.26.1

Solutions

CNA: This issue is fixed starting with version 1.26.1

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