CVE WatchJul 22, 2026

CVE-2026-55990

In NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-provider-cert:' files than there ar

CVSS

5.9

Medium

EPSS

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KEV

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Exploit Today

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0-100

Published: Jul 22, 2026 · Last modified: Jul 22, 2026 · CWE-457

EPSS · 30d

Not enough EPSS history yet.

Technical description

In NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-provider-cert:' files than there are matching 'dnscrypt-secret-key:' files, Unbound fills only the matched prefix and leaves the tail slots at the '0xdb' fill that libsodium's allocator writes into every allocation. Unbound would then iterate over the number of cert files, not the actual slots, so it walks into a slot with garbage data filled with '0xdb' bytes. Any unauthenticated client that sends one UDP datagram of ≥ 68 bytes whose first 8 bytes are '0xdb' to 'dnscrypt-port' will use that garbage entry which leads to a garbage dereference killing the server. This is a silent faulty configuration that goes unnoticed until triggered with the right client query. Unbound needs to be compiled with DNSCrypt support ('--enable-dnscrypt').

Official references

www.nlnetlabs.nlhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55990.txt

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