How severe is CVE-2026-26017?

CVE-2026-26017 has a CVSS score of 7.7/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-26017?

CVE-2026-26017 affects the following packages: github.com/coredns/coredns (Go). Ecosystems affected: Go.

How do I fix CVE-2026-26017?

Update github.com/coredns/coredns to 1.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-26017 is resolved across your whole dependency graph.

How do I detect CVE-2026-26017 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/coredns/coredns, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-26017 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-26017 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-26017 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-26017?

CVE-2026-26017 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 39th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-26017?

CVE-2026-26017 is classified as CWE-367 (CWE-367). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-26017 published, and has it been updated?

CVE-2026-26017 was published on March 6, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2026-26017 — coredns

HIGH

CVE-2026-26017 is a high-severity (CVSS 7.7) CWE-367 vulnerability in github.com/coredns/coredns. A fix is available for github.com/coredns/coredns — see the affected versions and patch details below.

CoreDNS ACL Bypass

Also known asGHSA-c9v3-4pv7-87prGO-2026-4630

Published

Mar 6, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-26017.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.02%

Lower risk than most CVEs39th percentile — riskier than 39% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-26017 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 383,485 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/coredns/coredns

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

In multi-tenant Kubernetes clusters, this flaw undermines DNS-based segmentation strategies.

Example scenario:

ACL blocks access to *.admin.svc.cluster.local
A rewrite rule maps public-name → admin.svc.cluster.local
An unprivileged pod queries public-name
ACL allows the request
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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/coredns/coredns`	all versions	1.14.2`go get github.com/coredns/coredns@v1.14.2`

Affected Products

1 product · 1 configurations

Application

corednscoredns.io

< 1.14.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/coredns/coredns, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/coredns/coredns to 1.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-26017 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-26017 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Advanced Cluster Management for Kubernetes 2.13	`rhacm2/lighthouse-agent-rhel9:1782924920`	RHSA-2026:36873
Red Hat Advanced Cluster Management for Kubernetes 2.14	`rhacm2/lighthouse-agent-rhel9:1780204232`	RHSA-2026:25127
Red Hat Advanced Cluster Management for Kubernetes 2.15	`rhacm2/lighthouse-coredns-rhel9:1774086225`	RHSA-2026:8151

Frequently Asked Questions

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 servic