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CoreDNS ACL Bypass

High severity GitHub Reviewed Published Mar 6, 2026 in coredns/coredns • Updated Mar 6, 2026

Package

gomod github.com/coredns/coredns (Go)

Affected versions

< 1.14.2

Patched versions

1.14.2

Description

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.

References

@yongtang yongtang published to coredns/coredns Mar 6, 2026
Published by the National Vulnerability Database Mar 6, 2026
Published to the GitHub Advisory Database Mar 6, 2026
Reviewed Mar 6, 2026
Last updated Mar 6, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(31st percentile)

Weaknesses

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. Learn more on MITRE.

CVE ID

CVE-2026-26017

GHSA ID

GHSA-c9v3-4pv7-87pr

Source code

Credits

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