{"id":"CVE-2026-56416","details":"In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form for an RRSIG-covered PX/RP/MINFO/SOA RRset, it computes the address of the second embedded domain name as 'datstart + dname_valid(datstart, ...)' and passes it straight to 'query_dname_tolower()' without checking that a second name is actually present in the RDATA. The wire-format parser accepts multi-dname RRs whose RDATA ends after the first name, so an attacker who runs a DNSSEC-signed authoritative server can deliver a record with an absent second domain name (e.g. SOA record) and cause 'query_dname_tolower()' to walk label-by-label through stale bytes in the per-worker 'env-\u003escratch_buffer', past the end of that heap allocation if 'msg-buffer-size' has been lowered from the default. This leads to heap buffer overflow and on a release build the outcome relies heavily on the contents of the buffer tail and the adjacent heap chunk.","modified":"2026-07-27T14:06:46.882602Z","published":"2026-07-22T14:17:22.090Z","related":["openSUSE-SU-2026:11380-1"],"references":[{"type":"ADVISORY","url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-56416.txt"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nlnetlabs/unbound","events":[{"introduced":"0"},{"fixed":"c33ad1b1a21e48bfe4f140e90252a9be1b0c5745"}],"database_specific":{"cpe":"cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*","extracted_events":[{"introduced":"0"},{"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","release-1.13.2rc1","release-1.13.1rc2","release-1.13.1","release-1.13.1rc1","release-1.13.0rc4","release-1.13.0rc3","release-1.13.0rc2","release-1.13.0rc1","release-1.12.0rc1","release-1.12.0","release-1.11.0rc1","release-1.11.0","1.11.0rc1","release-1.10.0rc2","release-1.10.0rc1","release-1.9.6","release-1.9.6rc1","release-1.9.3rc2","release-1.9.3","release-1.9.3rc1","release-1.9.2","release-1.9.2rc3","release-1.9.2rc1","release-1.9.2rc2","final-svn-state","release-1.9.1rc1","release-1.9.0rc1","release-1.8.2rc1","release-1.8.1rc1","release-1.8.0rc1","release-1.7.3rc1","release-1.7.2rc1","release-1.7.1rc1","release-1.7.0rc3","release-1.7.0rc2","release-1.7.0rc1","release-1.6.7","release-1.6.7rc1","release-1.6.6rc2","release-1.6.6rc1","release-1.6.4rc2","release-1.6.4rc1","release-1.6.2rc1","release-1.6.1rc3","release-1.6.1rc2","release-1.6.1rc1","release-1.6.0rc1","release-1.5.10rc1","release-1.5.10","release-1.5.9rc1","release-1.5.8rc1","release-1.5.8","release-1.5.7","release-1.5.6","release-1.5.6rc1","release-1.5.5","release-1.5.5rc1","release-1.5.4rc1","release-1.5.4","release-1.5.3rc1","release-1.5.2","release-1.5.2rc1","release-1.5.1","release-1.5.1rc2","release-1.5.1rc1","release-1.5.0rc1","release-1.4.22","release-1.4.22rc1","release-1.4.20","release-1.4.19","release-1.4.19rc1","release-1.4.18rc2","release-1.4.18rc1","release-1.4.17","release-1.4.17rc1","release-1.4.14","release-1.4.14rc1","release-1.4.13","release-1.4.13rc2","release-1.4.13rc1","release-1.4.12rc1","release-1.4.11rc3","release-1.4.11","release-1.4.11rc2","release-1.4.11rc1","release-1.4.9","release-1.4.9rc1","release-1.4.8rc1","release-1.4.7","release-1.4.7rc1","release-1.4.6","release-1.4.6rc1","release-1.4.5","release-1.4.5rc1","release-1.4.4","release-1.4.4rc1","release-1.4.3","release-1.4.2","release-1.4.1","release-1.4.0","release-1.4.0rc1","release-1.3.3","release-1.3.3rc1","release-1.3.2","release-1.3.1","release-1.1.1","release-1.0.1","release-0.11","release-0.10","release-0.8","release-0.7","release-0.6","release-0.5","release-0.4","release-0.3","release-0.1","release-0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-56416.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:L/A:L"}]}