CVE-2026-44621CWE-754

Libunbound applications configured with 'unwanted-reply-threshold' could eventually be abruptly terminated

Medium · published July 22, 2026

CVSS v3.1
5.9
EPSS
0%
Percentile
15.2
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
5.9 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00248 · 15.2th percentile
Weakness
CWE-754 · Improper Check for Unusual or Exceptional Conditions
Published
2026-07-22T13:06Z
EPSS history
Timeline
  • 22 JUL 13:06Z
    Libunbound applications configured with 'unwanted-reply-threshold' could eventually be abruptly terminated
    cvelistv5