CVE-2026-42944

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42944.txt	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*

History

20 May 2026, 22:50

Type	Values Removed	Values Added
First Time		Nlnetlabs Nlnetlabs unbound
References	~~() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42944.txt -~~	() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42944.txt - Mitigation, Vendor Advisory
CPE		cpe:2.3:a:nlnetlabs:unbound::::::::
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 7.5

20 May 2026, 10:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-05-20 10:16

Updated : 2026-05-20 22:50

NVD link : CVE-2026-42944

Mitre link : CVE-2026-42944

CVE.ORG link : CVE-2026-42944

JSON object : View

Products Affected

nlnetlabs

unbound

CWE

CWE-197

Numeric Truncation Error

CWE-787

Out-of-bounds Write

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