CVE-2026-44621: Nlnetlabs Unbound

Medium severity, CVSS 5.9. EPSS: 0.2% chance of exploitation in the next 30 days.

With NLnet Labs Unbound up to and including version 1.25.1, applications using libunbound and configured with 'unwanted-reply-threshold', could eventually be abruptly terminated if the threshold is reached and libunbound needs to call 'libworker_alloc_cleanup' since the function is absent from the function call allow list. When an application using libunbound sets 'unwanted-reply-threshold' to any non-zero value and the iterator queries an authoritative that replies with enough wrong-transaction-ID UDP datagrams to cross the threshold, the 'libworker_alloc_cleanup' will eventually be called. Since the function is absent from the function call allow list, this leads to a fatal exit of libunbound and eventual termination of the embedding application.Unbound itself is not affected since its relevant function 'worker_alloc_cleanup' is registed in the allow list and proceeds to perform the documented cache flush.

Affected products

• Nlnetlabs Unbound: before 1.25.2 (fixed in 1.25.2)

Published 2026-07-22. Last modified 2026-07-24.