Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 55.6%
CVSS Severity
CVSS v3 Score 9.8
Products affected by CVE-2026-33278
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cpe:2.3:a:nlnetlabs:unbound:1.19.1
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cpe:2.3:a:nlnetlabs:unbound:1.19.2
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cpe:2.3:a:nlnetlabs:unbound:1.19.3
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cpe:2.3:a:nlnetlabs:unbound:1.20.0
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cpe:2.3:a:nlnetlabs:unbound:1.21.0
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cpe:2.3:a:nlnetlabs:unbound:1.21.1
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cpe:2.3:a:nlnetlabs:unbound:1.22.0
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cpe:2.3:a:nlnetlabs:unbound:1.23.0
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cpe:2.3:a:nlnetlabs:unbound:1.23.1
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cpe:2.3:a:nlnetlabs:unbound:1.24.0
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cpe:2.3:a:nlnetlabs:unbound:1.24.1
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cpe:2.3:a:nlnetlabs:unbound:1.24.2
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cpe:2.3:a:nlnetlabs:unbound:1.25.0