CVE-2026-33278

CRITICAL EPSS 54.8%
Published May 20, 20261mo ago · Modified Jun 17, 20261w ago
9.1 CVSS 4.0
Critical
Find Similar
Published May 20, 2026 1mo ago
Last Modified Jun 17, 2026 1w ago

Description

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 Details

Base Score
9.1
Exploitability
—
Impact
—
Vector string
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Red
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
54.8% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 2

CWE-416 Use After Free Memory Safety
CWE-672

Affected Products 1

VendorProductVersionRange
nlnetlabsunbound*≥1.19.1  –  <1.25.1

References 1

  • nlnetlabs.nl https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt
    MitigationVendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.