GHSA-h8mm-c463-wjq3
HIGHGHSA-h8mm-c463-wjq3 is a high-severity (CVSS 7.5) vulnerability in github.com/coredns/coredns. O3 Security confirms whether GHSA-h8mm-c463-wjq3 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
CoreDNS' transfer stanza selection uses lexicographic compare (subzone ACL bypass)
Blast Radius
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Description
Summary
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/coredns/coredns | all versions | 1.14.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/coredns/coredns. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/coredns/coredns to 1.14.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-h8mm-c463-wjq3 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-h8mm-c463-wjq3 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-h8mm-c463-wjq3. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-h8mm-c463-wjq3 in your dependencies?
O3 detects GHSA-h8mm-c463-wjq3 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.