{"id":"CVE-2026-44687","details":"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).","modified":"2026-07-27T14:06:42.026114Z","published":"2026-07-22T14:17:19.040Z","related":["openSUSE-SU-2026:11380-1"],"references":[{"type":"ADVISORY","url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-44687.txt"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nlnetlabs/unbound","events":[{"introduced":"8e538dcaa8df2d0fab8ff3dcf94ac1f972450b66"},{"fixed":"c33ad1b1a21e48bfe4f140e90252a9be1b0c5745"}],"database_specific":{"cpe":"cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*","extracted_events":[{"introduced":"1.13.2"},{"fixed":"1.25.2"}],"source":"CPE_RANGE"}}],"versions":["release-1.25.1","release-1.25.0","release-1.25.0rc1","release-1.24.0","release-1.24.0rc1","release-1.23.0rc1","release-1.22.0","release-1.22.0rc1","release-1.21.0","release-1.21.0rc1","release-1.20.0rc1","release-1.20.0","release-1.19.3rc1","release-1.19.0rc1","release-1.19.0","release-1.18.0","release-1.18.0rc1","release-1.16.2","release-1.16.1rc1","release-1.16.1","release-1.16.0rc1","release-1.16.0","release-1.15.0rc1","release-1.15.0","release-1.14.0rc1","release-1.14.0","release-1.13.2"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-44687.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L"}]}