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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
Vendor advisory: debian — https://security-tracker.debian.org/tracker/CVE-2026-33278
Vendor advisory: suse — https://www.suse.com/security/cve/CVE-2026-33278.html
Vendor advisory: sep@nlnetlabs.nl — https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bookworm | affected | |
| debian | bullseye | affected | |
| debian | forky | fixed | 1.25.1-1 |
| debian | sid | fixed | 1.25.1-1 |
| debian | trixie | fixed | 1.22.0-2+deb13u3 |
Application impact
| Vendor | Product | Versions | Fixed |
|---|---|---|---|
| nlnetlabs | unbound | {"startIncluding":"1.19.1","endExcluding":"1.25.1"} | 1.25.1 |
References
CWEs
CWE-416 CWE-672
Verify integrity in audit chain (admin only). AS-IS.