CVE-2026-33489

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

1. Adjust COREDNS_BIN in the PoC to point at right path (see the top-level const definitions for tunables as well)
2. Run python3 ./acl-repro.py
3. 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.

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.

The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.

CVE-2026-33489 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.14.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-33489? CVE-2026-33489 is a high-severity missing authorization vulnerability in github.com/coredns/coredns (go), affecting versions < 1.14.3. It is fixed in 1.14.3. The application does not perform an authorization check before performing a sensitive operation.
2. How severe is CVE-2026-33489? CVE-2026-33489 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/coredns/coredns are affected by CVE-2026-33489? github.com/coredns/coredns (go) versions < 1.14.3 is affected.
4. Is there a fix for CVE-2026-33489? Yes. CVE-2026-33489 is fixed in 1.14.3. Upgrade to this version or later.
5. Is CVE-2026-33489 exploitable, and should I be worried? Whether CVE-2026-33489 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-33489 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-33489? Upgrade github.com/coredns/coredns to 1.14.3 or later.