Description
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| NLnet Labs | Unbound | < 1.25.1 | 1.25.1 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | unbound | 1.25.1-1 | — |
| Debian 13 | unbound | 1.22.0-2+deb13u3 | — |
| Debian 12 | unbound | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | unbound | 1.24.2-1ubuntu2.1 | — |
| Ubuntu 25.10 | unbound | 1.22.0-2ubuntu2.3 | — |
| Ubuntu 24.04 LTS | unbound | 1.19.2-1ubuntu3.8 | — |
| Ubuntu 22.04 LTS | unbound | 1.13.1-1ubuntu5.15 | — |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | unbound | No fix yet | — |
| Ubuntu Pro 18.04 LTS | unbound | No fix yet | — |
| Ubuntu Pro 16.04 LTS | unbound | No fix yet | — |
| Ubuntu Pro 14.04 LTS | unbound | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | unbound +6 | 1.26.1-2.el10_3 | RHSA-2026:97121 |
| RHEL 9 | unbound +4 | 1.26.1-1.el9_9 | RHSA-2026:97497 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | unbound +7 | 1.25.1-1.hum1 | RHSA-2026:20357 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | unbound +6 | 1.26.1-2.el10_3 | RLSA-2026:97121 |
| Rocky Linux 9 | unbound +4 | 1.26.1-1.el9_9 | RLSA-2026:97497 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP5 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
| SLES 15 SP4 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
Show 8 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | unbound | 1.24.1-160000.2.1 | SUSE-SU-2026:22160-1 |
| SLES for SAP 15 SP5 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
| SLES for SAP 15 SP4 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
| SLES 16.0 | unbound | 1.24.1-160000.2.1 | SUSE-SU-2026:22160-1 |
| SLE Micro 6.2 | unbound | 1.24.1-160000.2.1 | SUSE-SU-2026:22213-1 |
| SLE Micro 5.5 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
| SLE HPC 15 SP5 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
| SLE HPC 15 SP4 | unbound | 1.20.0-150100.10.25.1 | SUSE-SU-2026:2369-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | unbound | 1.25.1-1.1 | openSUSE-SU-2026:10903-1 |
| openSUSE Leap 16.0 | unbound | 1.24.1-160000.2.1 | openSUSE-SU-2026:21083-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | unbound | 1.25.1-r0 | — |
| Alpine v3.23 | unbound | 1.25.2-r0 | — |
| Alpine v3.22 | unbound | 1.25.2-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | unbound +5 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 |
| Amazon Linux 2 | unbound +4 | 1.7.3-15.amzn2.0.14 | ALAS2-2026-3322 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | unbound | 1.25.1-1 | — |
Advisories 14
- RHSA-2026:97497 Red Hat Security Advisory: unbound security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:97121 Red Hat Security Advisory: unbound security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RLSA-2026:97497 Moderate: unbound security, bug fix, and enhancement update Rocky Linux Security Advisories · Nov 13, 2026
- RLSA-2026:97121 Moderate: unbound security, bug fix, and enhancement update Rocky Linux Security Advisories · Nov 13, 2026
- WID-SEC-2026-2455 Oracle Solaris Drittanbieterkomponenten: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- WID-SEC-2026-1599 Unbound: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 10, 2026
- RHSA-2026:20357 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 9, 2026
- openSUSE-SU-2026:21083-1 Security update for unbound SUSE / openSUSE Security Updates · Jun 30, 2026
- SUSE-SU-2026:22160-1 Security update for unbound SUSE / openSUSE Security Updates · Jun 24, 2026
- SUSE-SU-2026:22213-1 Security update for unbound SUSE / openSUSE Security Updates · Jun 24, 2026
- SUSE-SU-2026:2369-1 Security update for unbound SUSE / openSUSE Security Updates · Jun 12, 2026
- ALAS2-2026-3322 Important: unbound security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Jun 8, 2026
- openSUSE-SU-2026:10903-1 libunbound8-1.25.1-1.1 on GA media SUSE / openSUSE Security Updates · May 30, 2026
- ALAS2023-2026-1756 Important: unbound security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · May 26, 2026
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42923.txt vendor-advisory