CVE-2026-26017: Github.com/coredns/coredns CoreDNS ACL Bypass Vulnerability

HIGH
Advisory Identifier: GHSA-c9v3-4pv7-87pr
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CVSS 7.7
CWE-367
Published
Advisory Summary

CVE-2026-26017 is a HIGH (CVSS 7.7) coredns acl bypass vulnerability (CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition) affecting Github.com/coredns/coredns libraries in the Go ecosystem. The issue involves coredns acl bypass. Remediation is available by upgrading affected packages to version 1.14.2.

CVE-2026-26017 at a Glance

CVE Identifier CVE-2026-26017
GHSA Identifier GHSA-c9v3-4pv7-87pr
Severity HIGH
CVSS v3.1 Base Score 7.7
CWE Classification CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
Affected Product Github.com/coredns/coredns
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 7.7

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-26017

To remediate this vulnerability, upgrade all affected Github.com/coredns/coredns dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/coredns/coredns fixed: 1.14.2 
Upgrade github.com/coredns/coredns to 1.14.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/coredns/coredns

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-26017, inspect your project dependencies for Github.com/coredns/coredns:

inspect dependencies for github.com/coredns/coredns

Analyze the terminal output to locate any version of Github.com/coredns/coredns in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.14.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition, where the product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. In Github.com/coredns/coredns, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

A logical vulnerability in CoreDNS allows DNS access controls to be bypassed due to the default execution order of plugins. Security plugins such as acl are evaluated before the rewrite plugin, resulting in a Time-of-Check Time-of-Use (TOCTOU) flaw. ### Impact In multi-tenant Kubernetes clusters, this flaw undermines DNS-based segmentation strategies. Example scenario: 1. ACL blocks access to *.admin.svc.cluster.local 2. A rewrite rule maps public-name → admin.svc.cluster.local 3. An unprivileged pod queries public-name 4. ACL allows the request 5. Rewrite exposes the internal admin service IP This allows unauthorized service discovery and reconnaissance of restricted internal infrastructure. ### Patches _Has the problem been patched? What versions should users upgrade to?_ ### Workarounds - Reorder the default plugin.cfg so that: - rewrite and other normalization plugins run before acl, opa, and firewall - Ensure all access control checks are applied after name normalization.

CVE-2026-26017 Affected Github.com/coredns/coredns Versions

1 component(s)
Fixed Versions:
1.14.2
Product / Package Ecosystem Affected Versions Fixed Version
github.com/coredns/coredns
golang/github.com/coredns/coredns
Go
< 1.14.2
1.14.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/coredns/coredns/security/advisories/GHSA-c9v3-4pv7-87pr
NVD — CVE-2026-26017 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-26017
Github.com/coredns/coredns Source Repository REPOSITORY
https://github.com/coredns/coredns
Github.com/coredns/coredns Release RELEASE
https://github.com/coredns/coredns/releases/tag/v1.14.2

Frequently Asked Questions

What is CVE-2026-26017?
CVE-2026-26017 is a security vulnerability in Github.com/coredns/coredns involving CoreDNS ACL Bypass under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition.
Which Github.com/coredns/coredns versions are affected?
Affected versions include releases prior to 1.14.2 across affected packages: github.com/coredns/coredns.
What version fixes CVE-2026-26017?
Upgrading to 1.14.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/coredns/coredns affected?
Yes, github.com/coredns/coredns is affected in releases prior to 1.14.2. Upgrade your dependency to 1.14.2 or later.
What is the CVSS score of CVE-2026-26017?
CVE-2026-26017 has a CVSS v3.1 base score of 7.7 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N.
What CWE is associated with CVE-2026-26017?
CVE-2026-26017 is classified under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition (The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.).
How can I check Go dependencies for CVE-2026-26017?
Run the dependency tree command: 'inspect dependencies for github.com/coredns/coredns'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c9v3-4pv7-87pr",
  "modified" : "2026-04-27T13:53:21Z",
  "published" : "2026-03-06T18:04:00Z",
  "aliases" : [ "CVE-2026-26017" ],
  "summary" : "CoreDNS ACL Bypass",
  "details" : "A logical vulnerability in CoreDNS allows DNS access controls to be bypassed due to the default execution order of plugins. Security plugins such as acl are evaluated before the rewrite plugin, resulting in a Time-of-Check Time-of-Use (TOCTOU) flaw.\n\n\n### Impact\n\nIn multi-tenant Kubernetes clusters, this flaw undermines DNS-based segmentation strategies.\n\nExample scenario:\n1. ACL blocks access to *.admin.svc.cluster.local\n2. A rewrite rule maps public-name → admin.svc.cluster.local\n3. An unprivileged pod queries public-name\n4. ACL allows the request\n5. Rewrite exposes the internal admin service IP\n\nThis allows unauthorized service discovery and reconnaissance of restricted internal infrastructure.\n\n### Patches\n_Has the problem been patched? What versions should users upgrade to?_\n\n### Workarounds\n\n- Reorder the default plugin.cfg so that:\n   - rewrite and other normalization plugins run before acl, opa, and firewall\n- Ensure all access control checks are applied after name normalization.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coredns/coredns"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.14.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/coredns/coredns/security/advisories/GHSA-c9v3-4pv7-87pr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26017"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/coredns/coredns"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coredns/coredns/releases/tag/v1.14.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-367" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-06T18:04:00Z",
    "nvd_published_at" : "2026-03-06T16:16:10Z"
  }
}