| Package | Affected versions | Patched versions |
|---|---|---|
| github.com/coredns/coredns | < 1.14.3 | 1.14.3 |
| coredns | < 1.14.3 | 1.14.3 |
CoreDNS' 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.
In 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:
So, a parent zone like example.org. can beat a child zone like a.example.org. purely due to lexicographic ordering ("example.org." > "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.
*** Candidate (add permissive parent transfer rule) *** axfr a.example.org.: rcode=0 ancount=5 (expected NOERROR=0 with ancount>0)
*** OK *** Subzone transfer ACL bypass reproduced: adding a permissive parent-zone stanza can override a stricter child-zone stanza due to lexicographic zone selection.
Unauthorized zone transfer can expose full zone contents to a remote network client that was intended to be denied by a subzone-specific transfer policy.
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