{"id":"DEBIAN-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":"2026-09-19T16:00:10.470983279Z","published":"2026-07-22T14:17:22.090Z","upstream":["CVE-2026-56416"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-56416"}],"affected":[{"package":{"name":"unbound","ecosystem":"Debian:12","purl":"pkg:deb/debian/unbound?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.17.1-2","1.17.1-2+deb12u1","1.17.1-2+deb12u2","1.17.1-2+deb12u3","1.17.1-2+deb12u4","1.17.1-2+loong64","1.18.0-1","1.18.0-2","1.19.1-1","1.19.2-1","1.20.0-1","1.21.1-1","1.22.0-1","1.22.0-2","1.23.1-1","1.24.0-1","1.24.0-2","1.24.1-1","1.24.1-2","1.24.2-1","1.25.0-1","1.25.1-1","1.25.2-1","1.26.0-1","1.26.0-2","1.26.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Debian:13","purl":"pkg:deb/debian/unbound?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.26.1-0+deb13u1"}]}],"versions":["1.22.0-2","1.22.0-2+deb13u1","1.22.0-2+deb13u2","1.22.0-2+deb13u3","1.23.1-1","1.24.0-1","1.24.0-2","1.24.1-1","1.24.1-2","1.24.2-1","1.25.0-1","1.25.1-1","1.25.2-1","1.26.0-1","1.26.0-2"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Debian:14","purl":"pkg:deb/debian/unbound?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.25.2-1"}]}],"versions":["1.22.0-2","1.23.1-1","1.24.0-1","1.24.0-2","1.24.1-1","1.24.1-2","1.24.2-1","1.25.0-1","1.25.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-56416.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L"}]}