GHSA-c9v3-4pv7-87pr CVE-2026-26017 GO-2026-4630
CoreDNS ACL Bypass
- Severity
- 7.7 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.40%
- Chance of exploitation in the next 30 days. Higher than 34.33% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
- Fix
1.14.2- Upgrade github.com/coredns/coredns to this version or later
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:
- 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 versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/coredns/coredns | < 1.14.2 |
1.14.2 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/coredns/coredns Go → 1.14.2
- go
go get github.com/coredns/coredns@v1.14.2 && go mod tidy
Severity breakdown
CVSS 3.1 7.7
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Weakness
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 to prevent it
- Implementation: The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
- Implementation: When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
- Architecture and Design: Limit the interleaving of operations on files from multiple processes.
- Implementation, Architecture and Design: If you cannot perform operations atomically and you must share access to the resource between multiple processes or threads, then try to limit the amount of time (CPU cycles) between the check and use of the resource. This will not fix the problem, but it could make it more difficult for an attack to succeed.
- Implementation: Recheck the resource after the use call to verify that the action was taken appropriately.
- Architecture and Design: Ensure that some environmental locking mechanism can be used to protect resources effectively.
- Implementation: Ensure that locking occurs before the check, as opposed to afterwards, such that the resource, as checked, is the same as it is when in use.
References
Advisories
Packages
Other links
- github.com/coredns/coredns/security/advisories/GHSA-c9v3-4pv7-87pr
- github.com/coredns/coredns/releases/tag/v1.14.2
- access.redhat.com/errata/RHSA-2026:25127
- access.redhat.com/errata/RHSA-2026:36873
- access.redhat.com/errata/RHSA-2026:8151
- access.redhat.com/security/cve/CVE-2026-26017
- bugzilla.redhat.com/show_bug.cgi
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-26017.json
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-9gm5-9rfh-m6vx CoreDNS DoH/DoQ/gRPC bypass UPDATE rejection enforced on UDP/TCP | High | Also affects github.com/coredns/coredns |
| GHSA-mrg3-qvqr-jw29 CoreDNS: Unauthenticated memory exhaustion in custom transports | High | Also affects github.com/coredns/coredns |
| GHSA-74w3-63xv-x9mv CoreDNS `k8s_external` headless AXFR can emit an empty transfer batch that panics the `transfer` plugin | Low | Also affects github.com/coredns/coredns |
| GHSA-vp29-5652-4fw9 CoreDNS has TSIG authentication bypass on gRPC and QUIC transports | Critical | Also affects github.com/coredns/coredns |
| GHSA-qhmp-q7xh-99rh CoreDNS has TSIG authentication bypass on DoT, DoH, DoH3, DoQ, and gRPC | High | Also affects github.com/coredns/coredns |
| GHSA-h8mm-c463-wjq3 CoreDNS' transfer stanza selection uses lexicographic compare (subzone ACL bypass) | High | Also affects github.com/coredns/coredns |
| GHSA-63cw-r7xf-jmwr CoreDNS DoH GET oversized dns= query parameter causes pre-validation CPU and memory amplification | High | Also affects github.com/coredns/coredns |
| GHSA-2wpx-qpw2-g5h5 CoreDNS' DoQ worker pool does not bound stream backlog | High | Also affects github.com/coredns/coredns |
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