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Vulnerability · Published May 20, 2026 · Assigned by NLnet Labs

CVE-2026-44608Use after free and crash under special conditions in RPZ code

Medium 4.6

In plain English

A medium-severity security flaw in Unbound from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)4.6Medium
Exploit odds (30 days)0.3%top 82.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.22unbound1.25.2-r0ALPINE-CVE-2026-44608
Alpine:v3.23unbound1.25.2-r0ALPINE-CVE-2026-44608
Alpine:v3.24unbound1.25.1-r0ALPINE-CVE-2026-44608
Debian:12unboundno fix listedDEBIAN-CVE-2026-44608
Debian:13unbound1.22.0-2+deb13u3DEBIAN-CVE-2026-44608
Debian:14unbound1.25.1-1DEBIAN-CVE-2026-44608
Ubuntu:24.04:LTSunbound1.19.2-1ubuntu3.8UBUNTU-CVE-2026-44608
Ubuntu:25.10unbound1.22.0-2ubuntu2.3UBUNTU-CVE-2026-44608
Ubuntu:26.04:LTSunbound1.24.2-1ubuntu2.1UBUNTU-CVE-2026-44608

Affected products (as reported)

VendorProductVersions
NLnet Labs Unbound 1.14.0 – before 1.25.1

Weakness: CWE-413 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

References