NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8282-1 Unbound vulnerabilities
Fixes

Solution

This issue is fixed starting with version 1.25.1


Workaround

No workaround given by the vendor.

History

Thu, 21 May 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Wed, 20 May 2026 23:00:00 +0000

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs unbound
CPEs cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*
Vendors & Products Nlnetlabs
Nlnetlabs unbound
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'}


Wed, 20 May 2026 14:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 20 May 2026 10:00:00 +0000

Type Values Removed Values Added
Description NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.
Title Heap overflow with multiple NSID, COOKIE, PADDING EDNS options
Weaknesses CWE-197
CWE-787
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Red'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: NLnet Labs

Published:

Updated: 2026-05-20T13:38:17.529Z

Reserved: 2026-05-07T10:07:51.833Z

Link: CVE-2026-42944

cve-icon Vulnrichment

Updated: 2026-05-20T13:37:37.199Z

cve-icon NVD

Status : Analyzed

Published: 2026-05-20T10:16:27.760

Modified: 2026-05-20T22:50:49.877

Link: CVE-2026-42944

cve-icon Redhat

Severity : Important

Publid Date: 2026-05-20T11:33:22Z

Links: CVE-2026-42944 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-05-21T08:15:06Z

Weaknesses