CVE-2026-33278

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.

How to fix CVE-2026-33278

To remediate CVE-2026-33278, upgrade the affected package to a fixed version below.

• —upgrade to 1.25.1-r0 or later
• —no fix listed

Is CVE-2026-33278 being exploited?

Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0, < 1.25.1-r0
• from 0

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2026-33278
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-33278