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

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

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.

Description from the National Vulnerability Database, published by sep@nlnetlabs.nl

What it means for a small business

If your business uses Unbound, install the vendor's update. If you're not sure whether you use it, ask whoever manages your computers.

How likely is an attack? The Exploit Prediction Scoring System, run by FIRST (the global association of security response teams), puts the odds of this one being exploited in the next 30 days at 1.4%, higher than 72% of CVEs. That’s above average: worth scheduling this week. Scored October 29, 2026, updated daily.

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Server check: what your web server says about itself, and whether that version has known flaws.

Sources

Part of the Huttenlocher Technologies vulnerability database, refreshed twice a day from CISA and the NVD. The title, category and plain-language guidance are ours; check the linked record before acting on a detail. This is general guidance, not a review of your systems.

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