CVE-2026-33278

NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables denial of service and possible remote code execution as a result of deep copying a data structure and erroneously overwriting a destination pointer. An adversary can exploit the vulnerability by controlling a malicious signed zone and querying a vulnerable Unbound. When DS sub-queries need to suspend validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1), Unbound deep-copies response messages to preserve them across memory region teardown. A struct-assignment bug overwrites the destination's pointer with the source's pointer. After the sub-query region is freed, the resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary code execution. Unbound 1.25.1 contains a patch with a fix to preserve the correct pointer when deep copying the data structure.

CVSS v3 9.8 CRITICAL

9.8^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

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

History

20 May 2026, 22:49

Type	Values Removed	Values Added
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 9.8
References	~~() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt -~~	() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt - Mitigation, Vendor Advisory
First Time		Nlnetlabs Nlnetlabs unbound
CPE		cpe:2.3:a:nlnetlabs:unbound::::::::

20 May 2026, 10:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-05-20 10:16

Updated : 2026-05-20 22:49

NVD link : CVE-2026-33278

Mitre link : CVE-2026-33278

CVE.ORG link : CVE-2026-33278

JSON object : View

Products Affected

nlnetlabs

unbound

CWE

CWE-416

Use After Free

CWE-672

Operation on a Resource after Expiration or Release

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