CVE-2026-23990: The Flux Operator is a Kubernetes CRD controller that manages the lifecycle of CNCF Flux CD and the ControlPlane enterprise distribution. Starting in ...

Description

The Flux Operator is a Kubernetes CRD controller that manages the lifecycle of CNCF Flux CD and the ControlPlane enterprise distribution. Starting in version 0.36.0 and prior to version 0.40.0, a privilege escalation vulnerability exists in the Flux Operator Web UI authentication code that allows an attacker to bypass Kubernetes RBAC impersonation and execute API requests with the operator's service account privileges. In order to be vulnerable, cluster admins must configure the Flux Operator with an OIDC provider that issues tokens lacking the expected claims (e.g., `email`, `groups`), or configure custom CEL expressions that can evaluate to empty values. After OIDC token claims are processed through CEL expressions, there is no validation that the resulting `username` and `groups` values are non-empty. When both values are empty, the Kubernetes client-go library does not add impersonation headers to API requests, causing them to be executed with the flux-operator service account's credentials instead of the authenticated user's limited permissions. This can result in privilege escalation, data exposure, and/or information disclosure. Version 0.40.0 patches the issue.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

0.30%

21.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Control-Plane	Flux Operator	>= 0.36.0, < 0.40.0

References

https://github.com/controlplaneio-fluxcd/flux-operator/commit/084540424f6de8ba5d88fb1fd1e8472ba29afd7ePatch
https://github.com/controlplaneio-fluxcd/flux-operator/pull/610Issue Tracking, Patch
https://github.com/controlplaneio-fluxcd/flux-operator/releases/tag/v0.40.0Product, Release Notes
https://github.com/controlplaneio-fluxcd/flux-operator/security/advisories/GHSA-4xh5-jcj2-ch8qMitigation, Vendor Advisory

Timeline

Published: Jan 21, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-23990?

The Flux Operator is a Kubernetes CRD controller that manages the lifecycle of CNCF Flux CD and the ControlPlane enterprise distribution. Starting in version 0.36.0 and prior to version 0.40.0, a privilege escalation vulnerability exists in the Flux Operator Web UI authentication code that allows an attacker to bypass Kubernetes RBAC impersonation and execute API requests with the operator's service account privileges. In order to be vulnerable, cluster admins must configure the Flux Operator with an OIDC provider that issues tokens lacking the expected claims (e.g., `email`, `groups`), or configure custom CEL expressions that can evaluate to empty values. After OIDC token claims are processed through CEL expressions, there is no validation that the resulting `username` and `groups` values are non-empty. When both values are empty, the Kubernetes client-go library does not add impersonation headers to API requests, causing them to be executed with the flux-operator service account's credentials instead of the authenticated user's limited permissions. This can result in privilege escalation, data exposure, and/or information disclosure. Version 0.40.0 patches the issue.

How severe is CVE-2026-23990?

CVE-2026-23990 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.30% probability of exploitation in the next 30 days.

How do I fix CVE-2026-23990?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.