# CVE-2026-44687: Off-by-one error in 'harden-below-nxdomain' logic can shadow a stub/forward zone by a legitimate parent's NXDOMAIN CVE-2026-44687 is fixed in 12 products on 1 platform, first by DEBIAN-CVE-2026-44687, released July 28, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-44687 - Priority: Routine - CVSS: 3.7 (Low) - EPSS: 0.0022 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jul 22, 2026 - Weakness: Off-by-one Error - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-44687 ## Description In NLnet Labs Unbound 1.13.2 up to and including 1.25.1, stub or forward zones where the name is below an intermediate labed below a DNSSEC signed zone could be shadowed by the intermediate label's secure NXDOMAIN answer from the parent. This is caused by an off-by-one error in 'harden-below-nxdomain' logic; enabled by default. It effectively bypasses the configuration and the configured stub/forward zone is never contacted. 'harden-below-nxdomain' does an upward DNS cache walk together with a delegation point guard that does not allow NXDOMAIN synthesis above stub/forward zones. The guard tests the domain name but before stripping a label. This results in an iteration where the domain name equals the configured stub/forward zone apex that passes the guard, strips one more label, and probes the cache at the apex's immediate public parent. If that parent has a cached DNSSEC-secure NXDOMAIN, which it will for any private namespace nested two or more labels under a signed public name, the walk returns it and the configured stub/forward upstream is never contacted. This can only be triggered by the query for the intermediate label (between the stub/forward apex and the DNSSEC parent zone). ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | python3-unbound amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | python3-unbound-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-44687](https://patchblox.com/security/data/fix/linux/debian-cve-2026-44687.md) | Jul 28, 2026 | | Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-44687](https://patchblox.com/security/data/fix/linux/debian-cve-2026-44687.md) | Jul 28, 2026 | | Linux | unbound amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 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 sles 15.6 | 1.25.2-150600.23.19.1 | [SUSE-SU-2026:3885-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3885-1.md) | Aug 31, 2026 | | Linux | unbound sles 15.7 | 1.25.2-150600.23.19.1 | [SUSE-SU-2026:3885-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3885-1.md) | Aug 31, 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 amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-anchor-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-debugsource amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-devel amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-libs amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-libs-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-utils amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | | Linux | unbound-utils-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.13 | [ALAS2023-2026-2033](https://patchblox.com/security/data/fix/linux/alas2023-2026-2033.md) | Aug 3, 2026 | --- Data as of 2026-11-09T19:38:12Z UTC. 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