Description
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the jostle logic that could defeat its purpose and degrade resolution performance. Retransmits of the same query could renew the age of slow running queries and not allow the jostle logic to see them as aged and potential targets for replacement with new queries. An adversary who can query a vulnerable Unbound and who can control a domain name server that replies slowly and/or maliciously to Unbound's queries can exploit the vulnerability and degrade the resolution performance of Unbound. When Unbound's 'num-queries-per-thread' reaches its limit, the jostle logic kicks in. When a new query comes in, half of the available queries that are also slow to resolve are candidates for replacement. The vulnerability then happens because duplicate queries that need resolution would skew the aging result by using the timestamp of the latest duplicate query instead of the original one that started the resolution effort. Cache and local data response performance remains unaffected. Coordinated attacks could raise this to a denial of resolution service. Unbound 1.25.1 contains a patch with a fix to attach an initial, non-updatable start time for incoming queries that allow the jostle logic to work as intended.
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 | 1.24.2-7.el10_2.2 | RHSA-2026:36320 |
| RHEL 9 | unbound +4 | 1.24.2-3.el9_8.2 | RHSA-2026:36777 |
| RHEL 8 | unbound +3 | 1.16.2-5.12.el8_10 | RHSA-2026:37282 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | unbound +7 | 1.25.1-2.hum1 | RHSA-2026:24013 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 10 | unbound +6 | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux 9 | unbound +4 | 1.24.2-3.el9_8.2 | ALSA-2026:36777 |
| AlmaLinux 8 | unbound +3 | 1.16.2-5.12.el8_10 | ALSA-2026:37282 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | unbound | 1.24.2-7.el10_2.2 | RLSA-2026:36320 |
| Rocky Linux 9 | unbound | 1.24.2-3.el9_8.2 | RLSA-2026:36777 |
| Rocky Linux 8 | unbound | 1.16.2-5.12.el8_10 | RLSA-2026:37282 |
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 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | unbound +6 | 1.24.2-7.el10_2.2 | ELSA-2026-36320 |
| Oracle Linux 9 | unbound +4 | 1.24.2-3.el9_8.2 | ELSA-2026-36777 |
| Oracle Linux 8 | unbound +3 | 1.16.2-5.12.el8_10 | ELSA-2026-37282 |
Advisories 22
- 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
- ALSA-2026:36777 Important: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:36320 Important: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:37282 Important: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- RHSA-2026:37282 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:36777 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:36320 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:24013 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 17, 2026
- RLSA-2026:36777 Important: unbound security update Rocky Linux Security Advisories · Jul 28, 2026
- RLSA-2026:36320 Important: unbound security update Rocky Linux Security Advisories · Jul 28, 2026
- RLSA-2026:37282 Important: unbound security update Rocky Linux Security Advisories · Jul 28, 2026
- ELSA-2026-36320 Important: unbound security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Jul 16, 2026
- ELSA-2026-36777 Important: unbound security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Jul 9, 2026
- ELSA-2026-37282 Important: unbound security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Jul 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-2026-42534.txt vendor-advisory