CVE-2026-23990

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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."}, {"lang": "es", "value": "El Flux Operator es un controlador CRD de Kubernetes que gestiona el ciclo de vida de CNCF Flux CD y la distribuci\u00f3n empresarial ControlPlane. A partir de la versi\u00f3n 0.36.0 y antes de la versi\u00f3n 0.40.0, existe una vulnerabilidad de escalada de privilegios en el c\u00f3digo de autenticaci\u00f3n de la interfaz de usuario web (Web UI) de Flux Operator que permite a un atacante eludir la suplantaci\u00f3n de identidad de Kubernetes RBAC y ejecutar solicitudes de API con los privilegios de la cuenta de servicio del operador. Para ser vulnerable, los administradores del cl\u00faster deben configurar el Flux Operator con un proveedor OIDC que emita tokens que carezcan de las reclamaciones esperadas (por ejemplo, 'email', 'groups'), o configurar expresiones CEL personalizadas que puedan evaluarse como valores vac\u00edos. Despu\u00e9s de que las reclamaciones del token OIDC se procesen a trav\u00e9s de expresiones CEL, no hay validaci\u00f3n de que los valores resultantes de 'username' y 'groups' no est\u00e9n vac\u00edos. Cuando ambos valores est\u00e1n vac\u00edos, la librer\u00eda client-go de Kubernetes no a\u00f1ade encabezados de suplantaci\u00f3n a las solicitudes de API, lo que hace que se ejecuten con las credenciales de la cuenta de servicio de flux-operator en lugar de los permisos limitados del usuario autenticado. Esto puede resultar en escalada de privilegios, exposici\u00f3n de datos y/o revelaci\u00f3n de informaci\u00f3n. La versi\u00f3n 0.40.0 corrige el problema."}], "id": "CVE-2026-23990", "lastModified": "2026-06-17T10:22:26.267", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N", "version": "3.1"}, "exploitabilityScore": 1.6, "impactScore": 3.6, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-23990", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-01-22T15:09:26.195880Z", "version": "2.0.3"}}]}, "published": "2026-01-21T23:15:52.930", "references": [{"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/controlplaneio-fluxcd/flux-operator/commit/084540424f6de8ba5d88fb1fd1e8472ba29afd7e"}, {"source": "security-advisories@github.com", "tags": ["Issue Tracking", "Patch"], "url": "https://github.com/controlplaneio-fluxcd/flux-operator/pull/610"}, {"source": "security-advisories@github.com", "tags": ["Product", "Release Notes"], "url": "https://github.com/controlplaneio-fluxcd/flux-operator/releases/tag/v0.40.0"}, {"source": "security-advisories@github.com", "tags": ["Mitigation", "Vendor Advisory"], "url": "https://github.com/controlplaneio-fluxcd/flux-operator/security/advisories/GHSA-4xh5-jcj2-ch8q"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-269"}, {"lang": "en", "value": "CWE-862"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

{"analysis": {"en": {"generated_at": "2026-04-18T04:05:37.630327+00:00", "value": {"mitigation_remediation": ["Upgrade the Flux Operator to version 0.40.0 or later, which includes the authentication patch.", "If an upgrade cannot be performed immediately, configure the OIDC provider to always supply non-empty email and groups claims, or enforce these validations before removing impersonation headers.", "Restrict access to the Flux Operator Web UI to trusted administrators and use network policies or firewall rules to limit exposure."], "summary": {"action": "Immediate Patch", "impact": "Privilege Escalation via Impersonation Bypass"}, "threat_synthesis": {"affected_systems": "The vulnerability affects the Flux Operator provided by controlplaneio-fluxcd. Versions starting from 0.36.0 up through the last release before 0.40.0 (i.e., 0.39.x) are vulnerable. Users running any of those versions should verify their installation and upgrade when possible.", "description_and_impact": "The Flux Operator Web UI contains a privilege escalation flaw that lets an attacker bypass Kubernetes RBAC impersonation, caused by unvalidated empty OIDC claim values. The vulnerability manifests when the OIDC provider returns missing email or groups or when custom CEL expressions evaluate to empty strings, resulting in no impersonation headers and execution under the operator\u2019s service account. This can lead to unauthorized API calls, data exposure, or information disclosure, as the attacker gains the full permissions of the operator\u2019s service account.", "risk_and_exploitability": "The CVSS score is 5.3, indicating moderate severity, while the EPSS score is below 1%, suggesting a low probability of exploitation at the time of this analysis. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires a misconfigured OIDC provider or CEL expressions that produce empty claim values; once triggered, an attacker can run API requests with the Flux Operator\u2019s service account privileges, bypassing all RBAC restrictions."}}}}, "created": "2026-01-22T10:08:21.365928+00:00", "updated": "2026-04-18T04:15:05.872116+00:00", "vendors": ["controlplaneio-fluxcd", "controlplaneio-fluxcd$PRODUCT$flux-operator"]}