CVE-2026-42959
Crash during DNSSEC validation of malicious content
CVE-2026-42959 is fixed in 17 products on 1 platform, first by libunbound2 1.6.7-1ubuntu2.6+esm4, released May 19, 2026. It is not reported as exploited. Patch Radar priority: High.
High
CVSS
8.1
Moderate
Exploitation
None reported
No vendor assessment
CISA KEV
Not listed
Not in the Known Exploited Vulnerabilities catalog
EPSS
0.0081
57th percentile
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| libunbound2 · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm4 | libunbound2 1.6.7-1ubuntu2.6+esm4 | May 19, 2026 |
| libunbound8 · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm1 | libunbound8 1.9.4-2ubuntu1.11+esm1 | May 19, 2026 |
| libunbound8 · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.15 | libunbound8 1.13.1-1ubuntu5.15 | May 27, 2026 |
| libunbound8 · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.8 | libunbound8 1.19.2-1ubuntu3.8 | May 27, 2026 |
| libunbound8 · Ubuntu 25.10 (questing) | 1.22.0-2ubuntu2.3 | libunbound8 1.22.0-2ubuntu2.3 | May 27, 2026 |
| libunbound8 · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.1 | libunbound8 1.24.2-1ubuntu2.1 | May 19, 2026 |
| python-unbound · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm4 | python-unbound 1.6.7-1ubuntu2.6+esm4 | May 19, 2026 |
| python-unbound · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm1 | python-unbound 1.9.4-2ubuntu1.11+esm1 | May 19, 2026 |
| python3-unbound · RHEL 8 | 0:1.16.2-5.11.el8_10 | RHSA-2026:24365 | Jun 24, 2026 |
| python3-unbound · RHEL 9 | 0:1.24.2-3.el9_8.1 | RHSA-2026:24369 | Jun 24, 2026 |
| python3-unbound · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm4 | python3-unbound 1.6.7-1ubuntu2.6+esm4 | May 19, 2026 |
| python3-unbound · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm1 | python3-unbound 1.9.4-2ubuntu1.11+esm1 | May 19, 2026 |
| python3-unbound · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.15 | python3-unbound 1.13.1-1ubuntu5.15 | May 27, 2026 |
| python3-unbound · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.8 | python3-unbound 1.19.2-1ubuntu3.8 | May 27, 2026 |
| python3-unbound · Ubuntu 25.10 (questing) | 1.22.0-2ubuntu2.3 | python3-unbound 1.22.0-2ubuntu2.3 | May 27, 2026 |
| python3-unbound · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.1 | python3-unbound 1.24.2-1ubuntu2.1 | May 19, 2026 |
| python3-unbound · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| python3-unbound · almalinux 8 | 1.16.2-5.11.el8_10 | ALSA-2026:24365 | Jun 8, 2026 |
| python3-unbound · almalinux 9 | 1.24.2-3.el9_8.1 | ALSA-2026:24369 | Jun 8, 2026 |
| python3-unbound · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| python3-unbound · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| python3-unbound · ol 8 | 0:1.16.2-5.11.el8_10 | ELSA-2026-24365 | Jun 8, 2026 |
| python3-unbound · ol 9 | 0:1.24.2-3.el9_8.1 | ELSA-2026-24369 | Jun 23, 2026 |
| python3-unbound-debuginfo · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound · Debian 13.5 (trixie) | 1.22.0-2+deb13u3 | DEBIAN-CVE-2026-42959 | May 27, 2026 |
| unbound · Debian 14 | 1.25.1-1 | DEBIAN-CVE-2026-42959 | May 27, 2026 |
| unbound · RHEL 10 | 1.24.2-7.el10_2.1 | RHSA-2026:23231 | May 20, 2026 |
| unbound · RHEL 8 | 0:1.16.2-5.11.el8_10 | RHSA-2026:24365 | Jun 24, 2026 |
| unbound · RHEL 9 | 0:1.24.2-3.el9_8.1 | RHSA-2026:24369 | Jun 24, 2026 |
| unbound · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm4 | unbound 1.6.7-1ubuntu2.6+esm4 | May 19, 2026 |
| unbound · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm1 | unbound 1.9.4-2ubuntu1.11+esm1 | May 19, 2026 |
| unbound · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.15 | unbound 1.13.1-1ubuntu5.15 | May 27, 2026 |
| unbound · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.8 | unbound 1.19.2-1ubuntu3.8 | May 27, 2026 |
| unbound · Ubuntu 25.10 (questing) | 1.22.0-2ubuntu2.3 | unbound 1.22.0-2ubuntu2.3 | May 27, 2026 |
| unbound · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.1 | unbound 1.24.2-1ubuntu2.1 | May 19, 2026 |
| unbound · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| unbound · almalinux 8 | 1.16.2-5.11.el8_10 | ALSA-2026:24365 | Jun 8, 2026 |
| unbound · almalinux 9 | 1.24.2-3.el9_8.1 | ALSA-2026:24369 | Jun 8, 2026 |
| unbound · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| unbound · ol 8 | 0:1.16.2-5.11.el8_10 | ELSA-2026-24365 | Jun 8, 2026 |
| unbound · ol 9 | 0:1.24.2-3.el9_8.1 | ELSA-2026-24369 | Jun 23, 2026 |
| unbound · opensuse-leap 16.0 | 1.24.1-160000.2.1 | OPENSUSE-SU-2026:21083-1 | Jun 18, 2026 |
| unbound · rocky 10 | 0:1.24.2-7.el10_2.1 | RLSA-2026:23231 | Jun 6, 2026 |
| unbound · rocky 8 | 0:1.16.2-5.11.el8_10 | RLSA-2026:24365 | Jun 11, 2026 |
| unbound · rocky 9 | 0:1.24.2-3.el9_8.1 | RLSA-2026:24369 | Jun 11, 2026 |
| unbound · sles 16.0 | 1.24.1-160000.2.1 | SUSE-SU-2026:22160-1 | Jun 18, 2026 |
| unbound-anchor · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm4 | unbound-anchor 1.6.7-1ubuntu2.6+esm4 | May 19, 2026 |
| unbound-anchor · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm1 | unbound-anchor 1.9.4-2ubuntu1.11+esm1 | May 19, 2026 |
| unbound-anchor · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.15 | unbound-anchor 1.13.1-1ubuntu5.15 | May 27, 2026 |
| unbound-anchor · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.8 | unbound-anchor 1.19.2-1ubuntu3.8 | May 27, 2026 |
| unbound-anchor · Ubuntu 25.10 (questing) | 1.22.0-2ubuntu2.3 | unbound-anchor 1.22.0-2ubuntu2.3 | May 27, 2026 |
| unbound-anchor · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.1 | unbound-anchor 1.24.2-1ubuntu2.1 | May 19, 2026 |
| unbound-anchor · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| unbound-anchor · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-anchor · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| unbound-anchor-debuginfo · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-debuginfo · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-debugsource · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-devel · RHEL 8 | 0:1.16.2-5.11.el8_10 | RHSA-2026:24365 | Jun 24, 2026 |
| unbound-devel · RHEL 9 | 0:1.24.2-3.el9_8.1 | RHSA-2026:24369 | Jun 24, 2026 |
| unbound-devel · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| unbound-devel · almalinux 8 | 1.16.2-5.11.el8_10 | ALSA-2026:24365 | Jun 8, 2026 |
| unbound-devel · almalinux 9 | 1.24.2-3.el9_8.1 | ALSA-2026:24369 | Jun 8, 2026 |
| unbound-devel · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-devel · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| unbound-devel · ol 8 | 0:1.16.2-5.11.el8_10 | ELSA-2026-24365 | Jun 8, 2026 |
| unbound-devel · ol 9 | 0:1.24.2-3.el9_8.1 | ELSA-2026-24369 | Jun 23, 2026 |
| unbound-dracut · RHEL 9 | 0:1.24.2-3.el9_8.1 | RHSA-2026:24369 | Jun 24, 2026 |
| unbound-dracut · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| unbound-dracut · almalinux 9 | 1.24.2-3.el9_8.1 | ALSA-2026:24369 | Jun 8, 2026 |
| unbound-dracut · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| unbound-dracut · ol 9 | 0:1.24.2-3.el9_8.1 | ELSA-2026-24369 | Jun 23, 2026 |
| unbound-host · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm4 | unbound-host 1.6.7-1ubuntu2.6+esm4 | May 19, 2026 |
| unbound-host · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm1 | unbound-host 1.9.4-2ubuntu1.11+esm1 | May 19, 2026 |
| unbound-host · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.15 | unbound-host 1.13.1-1ubuntu5.15 | May 27, 2026 |
| unbound-host · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.8 | unbound-host 1.19.2-1ubuntu3.8 | May 27, 2026 |
| unbound-host · Ubuntu 25.10 (questing) | 1.22.0-2ubuntu2.3 | unbound-host 1.22.0-2ubuntu2.3 | May 27, 2026 |
| unbound-host · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.1 | unbound-host 1.24.2-1ubuntu2.1 | May 19, 2026 |
| unbound-libs · RHEL 8 | 0:1.16.2-5.11.el8_10 | RHSA-2026:24365 | Jun 24, 2026 |
| unbound-libs · RHEL 9 | 0:1.24.2-3.el9_8.1 | RHSA-2026:24369 | Jun 24, 2026 |
| unbound-libs · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| unbound-libs · almalinux 8 | 1.16.2-5.11.el8_10 | ALSA-2026:24365 | Jun 8, 2026 |
| unbound-libs · almalinux 9 | 1.24.2-3.el9_8.1 | ALSA-2026:24369 | Jun 8, 2026 |
| unbound-libs · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-libs · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| unbound-libs · ol 8 | 0:1.16.2-5.11.el8_10 | ELSA-2026-24365 | Jun 8, 2026 |
| unbound-libs · ol 9 | 0:1.24.2-3.el9_8.1 | ELSA-2026-24369 | Jun 23, 2026 |
| unbound-libs-debuginfo · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-utils · almalinux 10 | 1.24.2-7.el10_2.1 | ALSA-2026:23231 | Jun 4, 2026 |
| unbound-utils · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
| unbound-utils · ol 10 | 0:1.24.2-7.el10_2.2 | ELSA-2026-23231 | Jul 21, 2026 |
| unbound-utils-debuginfo · amzn 2023 | 1.17.1-1.amzn2023.0.12 | ALAS2023-2026-1756 | May 25, 2026 |
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