Nlnetlabs Unbound
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.
What this means for your business
- It affects Nlnetlabs Unbound. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
- FIRST's prediction model gives it a 1% chance of attack attempts being seen in the next 30 days, ranking above 68% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Nlnetlabs Unbound, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Not sure if your company is exposed?
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Scoring
- CVSS
- 9.8 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H- CVSS v4
- 9.1
- Weakness
- CWE-416
- Assigned by
- sep@nlnetlabs.nl
Dates
- Published
- 2026-05-20
- Last modified
- 2026-08-25
- Sources
- NVD
Affected products
- Nlnetlabs Unbound1.19.1 - 1.25.1
As listed in the NVD configuration data. Not a statement about your estate.
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt
- https://access.redhat.com/errata/RHSA-2026:19752
- https://access.redhat.com/errata/RHSA-2026:23231
- https://access.redhat.com/errata/RHSA-2026:24369
- https://access.redhat.com/security/cve/CVE-2026-33278
- https://bugzilla.redhat.com/show_bug.cgi?id=2479808
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33278.json