GHSA-H8MM-C463-WJQ3
Vulnerability from github – Published: 2026-04-28 22:44 – Updated: 2026-05-08 15:28Summary
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.
Details
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: - zone := "" // longest zone match wins (plugin/transfer/transfer.go) - if z > zone { zone = z; x = xfr } (plugin/transfer/transfer.go)
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.
PoC
- Adjust COREDNS_BIN in the PoC to point at right path (see the top-level const definitions for tunables as well)
- Run python3 ./acl-repro.py
- Expected output: *** Baseline (only subzone transfer rule) *** axfr a.example.org.: rcode=5 ancount=0 (expected REFUSED=5)
*** 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.
Impact
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.
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "github.com/coredns/coredns"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.14.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-33489"
],
"database_specific": {
"cwe_ids": [
"CWE-862",
"CWE-863"
],
"github_reviewed": true,
"github_reviewed_at": "2026-04-28T22:44:39Z",
"nvd_published_at": "2026-05-05T20:16:36Z",
"severity": "HIGH"
},
"details": "### Summary\nCoreDNS\u0027 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.",
"id": "GHSA-h8mm-c463-wjq3",
"modified": "2026-05-08T15:28:38Z",
"published": "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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
},
{
"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",
"type": "CVSS_V4"
}
],
"summary": "CoreDNS\u0027 transfer stanza selection uses lexicographic compare (subzone ACL bypass)"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.