Possible ZONEMD verification bypass window

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77955
StatePUBLISHED
AssignerNLnet Labs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 09:17:05 UTC
Updated2026-09-23 20:19:28 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 4.4 MEDIUM from [email protected]

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

EPSS: 0.001500000 probability, percentile 0.034780000 (date 2026-09-24)

Problem Types: CWE-345 | CWE-345 CWE-345: Insufficient Verification of Data Authenticity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.4MEDIUMCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N
3.1CNACVSS4.4MEDIUMCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

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

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

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 1.13.2 1.26.1 semver Not specified

References

ReferenceSourceLinkTags
www.nlnetlabs.nl/downloads/unbound/CVE-2026-77955.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: Yuqi Qiu (Nankai University, AOSP Lab) (en)

CNA: Xiang Li (Nankai University, AOSP Lab) (en)

CNA: Qifan Zhang (Palo Alto Networks) (en)

Additional Advisory Data

SourceTimeEvent
CNA2026-08-11T00:00:00.000ZIssue reported by Yuqi Qiu
CNA2026-08-16T00:00:00.000ZIssue reported by Qifan Zhang
CNA2026-08-19T00:00:00.000ZNLnet Labs shares patch with Yuqi Qiu
CNA2026-08-20T00:00:00.000ZYuqi Qiu verifies patch
CNA2026-09-01T00:00:00.000ZNLnet Labs shares patch with Qifan Zhang
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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