{"id":"GHSA-h8mm-c463-wjq3","summary":"CoreDNS' transfer stanza selection uses lexicographic compare (subzone ACL bypass)","details":"### Summary\nCoreDNS' transfer plugin can select the wrong ACL stanza when both a parent zone and a more-specific subzone are configured. A permissive parent-zone transfer rule can override a restrictive subzone rule (name-dependent), allowing an unauthorized client to perform AXFR/IXFR for the subzone and retrieve its zone contents.\n\n### Details\nIn plugin/transfer/transfer.go, stanza selection is implemented by longestMatch(), which is documented as \"longest zone match wins\", but it actually chooses the winner via a lexicographic string comparison:\n- zone := \"\" // longest zone match wins (plugin/transfer/transfer.go)\n- if z \u003e zone { zone = z; x = xfr } (plugin/transfer/transfer.go)\n\nSo, a parent zone like example.org. can beat a child zone like a.example.org. purely due to lexicographic ordering (\"example.org.\" \u003e \"a.example.org.\"), even though the child zone is the longer/more specific suffix match. The bypass is data-dependent (some child labels will win, some will lose), making it operationally non-intuitive.\n\n### PoC\n1. Adjust COREDNS_BIN in the PoC to point at right path (see the top-level const definitions for tunables as well)\n2. Run python3 ./acl-repro.py\n3. Expected output:\n*** Baseline (only subzone transfer rule) ***\naxfr a.example.org.: rcode=5 ancount=0 (expected REFUSED=5)\n\n*** Candidate (add permissive parent transfer rule) ***\naxfr a.example.org.: rcode=0 ancount=5 (expected NOERROR=0 with ancount\u003e0)\n\n*** OK ***\nSubzone transfer ACL bypass reproduced: adding a permissive parent-zone stanza can override a stricter child-zone stanza due to lexicographic zone selection.\n\n### Impact\nUnauthorized zone transfer can expose full zone contents to a remote network client that was intended to be denied by a subzone-specific transfer policy.","aliases":["CVE-2026-33489","GO-2026-5417"],"modified":"2026-07-17T21:08:51.785178666Z","published":"2026-04-28T22:44:39Z","database_specific":{"nvd_published_at":"2026-05-05T20:16:36Z","cwe_ids":["CWE-862","CWE-863"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-04-28T22:44:39Z"},"references":[{"type":"WEB","url":"https://github.com/coredns/coredns/security/advisories/GHSA-h8mm-c463-wjq3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33489"},{"type":"PACKAGE","url":"https://github.com/coredns/coredns"},{"type":"WEB","url":"https://github.com/coredns/coredns/releases/tag/v1.14.3"}],"affected":[{"package":{"name":"github.com/coredns/coredns","ecosystem":"Go","purl":"pkg:golang/github.com/coredns/coredns"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.14.3"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-h8mm-c463-wjq3/GHSA-h8mm-c463-wjq3.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"}]}