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

CVE-2026-44390Unbounded name compression in certain cases causes degradation of service

High 7.5

In plain English

A high-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 0.6% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.6%top 48.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability when handling replies with very large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very large RRsets with records that don't share a suffix above the root can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for this but it didn't account for the case where records would not share any suffix above the root. That causes Unbound to go in a different code path because of the compression tree lookup failure and eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch with a fix that increments the compression counter regardless of the compression tree lookup. This is a complement fix to CVE-2024-8508.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:10python3-unbound1.24.2-7.el10_2.2ALSA-2026:36320
AlmaLinux:8python3-unbound1.16.2-5.12.el8_10ALSA-2026:37282
AlmaLinux:9python3-unbound1.24.2-3.el9_8.2ALSA-2026:36777
AlmaLinux:10unbound1.24.2-7.el10_2.2ALSA-2026:36320
AlmaLinux:8unbound1.16.2-5.12.el8_10ALSA-2026:37282
AlmaLinux:9unbound1.24.2-3.el9_8.2ALSA-2026:36777
AlmaLinux:10unbound-anchor1.24.2-7.el10_2.2ALSA-2026:36320
AlmaLinux:10unbound-devel1.24.2-7.el10_2.2ALSA-2026:36320
AlmaLinux:8unbound-devel1.16.2-5.12.el8_10ALSA-2026:37282
AlmaLinux:9unbound-devel1.24.2-3.el9_8.2ALSA-2026:36777
AlmaLinux:10unbound-dracut1.24.2-7.el10_2.2ALSA-2026:36320
AlmaLinux:9unbound-dracut1.24.2-3.el9_8.2ALSA-2026:36777
AlmaLinux:10unbound-libs1.24.2-7.el10_2.2ALSA-2026:36320
AlmaLinux:8unbound-libs1.16.2-5.12.el8_10ALSA-2026:37282
AlmaLinux:9unbound-libs1.24.2-3.el9_8.2ALSA-2026:36777
AlmaLinux:10unbound-utils1.24.2-7.el10_2.2ALSA-2026:36320
Alpine:v3.22unbound1.25.2-r0ALPINE-CVE-2026-44390
Alpine:v3.23unbound1.25.2-r0ALPINE-CVE-2026-44390
Alpine:v3.24unbound1.25.1-r0ALPINE-CVE-2026-44390
Debian:12unboundno fix listedDEBIAN-CVE-2026-44390
Debian:13unbound1.22.0-2+deb13u3DEBIAN-CVE-2026-44390
Debian:14unbound1.25.1-1DEBIAN-CVE-2026-44390
Rocky Linux:10unbound0:1.24.2-7.el10_2.2RLSA-2026:36320
Rocky Linux:8unbound0:1.16.2-5.12.el8_10RLSA-2026:37282
Rocky Linux:9unbound0:1.24.2-3.el9_8.2RLSA-2026:36777
Ubuntu:22.04:LTSunbound1.13.1-1ubuntu5.15UBUNTU-CVE-2026-44390
Ubuntu:24.04:LTSunbound1.19.2-1ubuntu3.8UBUNTU-CVE-2026-44390
Ubuntu:25.10unbound1.22.0-2ubuntu2.3UBUNTU-CVE-2026-44390
Ubuntu:26.04:LTSunbound1.24.2-1ubuntu2.1UBUNTU-CVE-2026-44390

Affected products (as reported)

VendorProductVersions
NLnet Labs Unbound 0 – before 1.25.1

Weakness: CWE-407, CWE-1050 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References