# CVE-2026-55973: 'dns-error-reporting: yes' leads to stack buffer overflow CVE-2026-55973 is fixed in 9 products on 1 platform, first by DEBIAN-CVE-2026-55973, released July 28, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-55973 - Priority: High - CVSS: 8.6 (Moderate) - EPSS: 0.0028 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jul 22, 2026 - Weakness: Improper Input Validation - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55973 ## Description In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | libunbound8 Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [libunbound8 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libunbound8-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | python3-unbound RHEL 9 | 0:1.24.2-3.el9_8.4 | [RHSA-2026:55841](https://patchblox.com/security/data/fix/linux/rhsa-2026-55841.md) | Aug 19, 2026 | | Linux | python3-unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [python3-unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-python3-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | python3-unbound almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | python3-unbound almalinux 9 | 1.24.2-3.el9_8.4 | [ALSA-2026:55841](https://patchblox.com/security/data/fix/linux/alsa-2026-55841.md) | Aug 17, 2026 | | Linux | python3-unbound ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | | Linux | python3-unbound ol 9 | 0:1.24.2-3.el9_8.4 | [ELSA-2026-55841](https://patchblox.com/security/data/fix/linux/elsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-55973](https://patchblox.com/security/data/fix/linux/debian-cve-2026-55973.md) | Jul 28, 2026 | | Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-55973](https://patchblox.com/security/data/fix/linux/debian-cve-2026-55973.md) | Jul 28, 2026 | | Linux | unbound RHEL 10 | 1.24.2-7.el10_2.4 | [RHSA-2026:55892](https://patchblox.com/security/data/fix/linux/rhsa-2026-55892.md) | Aug 18, 2026 | | Linux | unbound RHEL 9 | 0:1.24.2-3.el9_8.4 | [RHSA-2026:55841](https://patchblox.com/security/data/fix/linux/rhsa-2026-55841.md) | Aug 19, 2026 | | Linux | unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound almalinux 9 | 1.24.2-3.el9_8.4 | [ALSA-2026:55841](https://patchblox.com/security/data/fix/linux/alsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound ol 9 | 0:1.24.2-3.el9_8.4 | [ELSA-2026-55841](https://patchblox.com/security/data/fix/linux/elsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound opensuse-leap 16.0 | 1.25.2-160000.1.1 | [OPENSUSE-SU-2026:21550-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21550-1.md) | Aug 10, 2026 | | Linux | unbound rocky 10 | 0:1.24.2-7.el10_2.4 | [RLSA-2026:55892](https://patchblox.com/security/data/fix/linux/rlsa-2026-55892.md) | Aug 18, 2026 | | Linux | unbound rocky 9 | 0:1.24.2-3.el9_8.4 | [RLSA-2026:55841](https://patchblox.com/security/data/fix/linux/rlsa-2026-55841.md) | Aug 18, 2026 | | Linux | unbound sles 16.0 | 1.25.2-160000.1.1 | [SUSE-SU-2026:23226-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23226-1.md) | Aug 10, 2026 | | Linux | unbound-anchor Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-anchor 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-anchor-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound-anchor almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-anchor ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-devel RHEL 9 | 0:1.24.2-3.el9_8.4 | [RHSA-2026:55841](https://patchblox.com/security/data/fix/linux/rhsa-2026-55841.md) | Aug 19, 2026 | | Linux | unbound-devel almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-devel almalinux 9 | 1.24.2-3.el9_8.4 | [ALSA-2026:55841](https://patchblox.com/security/data/fix/linux/alsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound-devel ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-devel ol 9 | 0:1.24.2-3.el9_8.4 | [ELSA-2026-55841](https://patchblox.com/security/data/fix/linux/elsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound-dracut RHEL 9 | 0:1.24.2-3.el9_8.4 | [RHSA-2026:55841](https://patchblox.com/security/data/fix/linux/rhsa-2026-55841.md) | Aug 19, 2026 | | Linux | unbound-dracut almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-dracut almalinux 9 | 1.24.2-3.el9_8.4 | [ALSA-2026:55841](https://patchblox.com/security/data/fix/linux/alsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound-dracut ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-dracut ol 9 | 0:1.24.2-3.el9_8.4 | [ELSA-2026-55841](https://patchblox.com/security/data/fix/linux/elsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound-host Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-host 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-host-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound-libs RHEL 9 | 0:1.24.2-3.el9_8.4 | [RHSA-2026:55841](https://patchblox.com/security/data/fix/linux/rhsa-2026-55841.md) | Aug 19, 2026 | | Linux | unbound-libs almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-libs almalinux 9 | 1.24.2-3.el9_8.4 | [ALSA-2026:55841](https://patchblox.com/security/data/fix/linux/alsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound-libs ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-libs ol 9 | 0:1.24.2-3.el9_8.4 | [ELSA-2026-55841](https://patchblox.com/security/data/fix/linux/elsa-2026-55841.md) | Aug 17, 2026 | | Linux | unbound-utils almalinux 10 | 1.24.2-7.el10_2.4 | [ALSA-2026:55892](https://patchblox.com/security/data/fix/linux/alsa-2026-55892.md) | Aug 17, 2026 | | Linux | unbound-utils ol 10 | 0:1.24.2-7.el10_2.4 | [ELSA-2026-55892](https://patchblox.com/security/data/fix/linux/elsa-2026-55892.md) | Aug 17, 2026 | --- Data as of 2026-11-08T13:06:02Z UTC. 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