Description
NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.
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 | 1.9.4-2ubuntu1.11+esm1 | — |
| Ubuntu Pro 18.04 LTS | unbound | 1.6.7-1ubuntu2.6+esm4 | — |
| Ubuntu Pro 16.04 LTS | unbound | 1.5.8-1ubuntu1.1+esm3 | — |
| Ubuntu Pro 14.04 LTS | unbound | 1.4.22-1ubuntu4.14.04.3+esm3 | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | unbound +6 | 1.24.2-7.el10_2.1 | RHSA-2026:23231 |
| RHEL 9 | unbound +4 | 1.24.2-3.el9_8.1 | RHSA-2026:24369 |
| RHEL 8 | unbound +3 | 1.16.2-5.11.el8_10 | RHSA-2026:24365 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | unbound +7 | 1.25.1-0.1.hum1 | RHSA-2026:19752 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 10 | unbound +6 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 |
| AlmaLinux 9 | unbound +4 | 1.24.2-3.el9_8.1 | ALSA-2026:24369 |
| AlmaLinux 8 | unbound +3 | 1.16.2-5.11.el8_10 | ALSA-2026:24365 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | unbound | 1.24.2-7.el10_2.1 | RLSA-2026:23231 |
| Rocky Linux 9 | unbound | 1.24.2-3.el9_8.1 | RLSA-2026:24369 |
| Rocky Linux 8 | unbound | 1.16.2-5.11.el8_10 | RLSA-2026:24365 |
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-2026-23231 |
| Oracle Linux 9 | unbound +4 | 1.24.2-3.el9_8.1 | ELSA-2026-24369 |
| Oracle Linux 8 | unbound +3 | 1.16.2-5.11.el8_10 | ELSA-2026-24365 |
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-2026:24369 Important: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:23231 Important: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:24365 Important: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- RHSA-2026:24369 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:24365 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:23231 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:19752 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 6, 2026
- ELSA-2026-23231 Important: unbound security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Jul 21, 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
- ELSA-2026-24369 Important: unbound security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Jun 23, 2026
- SUSE-SU-2026:2369-1 Security update for unbound SUSE / openSUSE Security Updates · Jun 12, 2026
- RLSA-2026:24369 Important: unbound security update Rocky Linux Security Advisories · Jun 11, 2026
- RLSA-2026:24365 Important: unbound security update Rocky Linux Security Advisories · Jun 11, 2026
- ALAS2-2026-3322 Important: unbound security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Jun 8, 2026
- ELSA-2026-24365 Important: unbound security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Jun 8, 2026
- RLSA-2026:23231 Important: unbound security update Rocky Linux Security Advisories · Jun 6, 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-2026-42959.txt vendor-advisory