Vulnerability Details CVE-2026-42944
NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 18.8%
CVSS Severity
CVSS v3 Score 7.5
Products affected by CVE-2026-42944
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cpe:2.3:a:nlnetlabs:unbound:1.14.0
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cpe:2.3:a:nlnetlabs:unbound:1.15.0
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cpe:2.3:a:nlnetlabs:unbound:1.16.0
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cpe:2.3:a:nlnetlabs:unbound:1.16.1
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cpe:2.3:a:nlnetlabs:unbound:1.16.2
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cpe:2.3:a:nlnetlabs:unbound:1.16.3
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cpe:2.3:a:nlnetlabs:unbound:1.17.0
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cpe:2.3:a:nlnetlabs:unbound:1.17.1
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cpe:2.3:a:nlnetlabs:unbound:1.18.0
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cpe:2.3:a:nlnetlabs:unbound:1.19.0
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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