Review reviewCritical

CVE-2026-33278

NLnet Labs Unbound, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9

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 s...

CVSS: 9.1
EPSS: 1.27%
CISA KEV: Not listed
Published: 2026.05.20

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability1.27%

Technical severityCVSS 9.1

Vulnerability overview

Affected product and versions

Product: NLnet Labs Unbound, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9
Affected versions: >= 1.19.1 < 1.25.1
Fixed versions: 1.25.1

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that NLnet Labs Unbound, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: 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
CWE: CWE-416, CWE-672