Enterprise Kubernetes administrators and OpenShift platform engineers are facing urgent security advisories following disclosures of a maximum-severity privilege escalation vulnerability in Red Hat Advanced Cluster Management for Kubernetes (ACM). Tracked as CVE-2026-10090 (CVSS score 9.9/10.0), the flaw allows low-privileged, namespace-scoped users to bypass authorization checks and elevate their access to full cluster-admin across the entire Kubernetes hub environment.

Deconstructing the Application Subscription Controller Flaw

Red Hat ACM relies on the Application Subscription controller (multicluster-operators-subscription) to automate workload deployment across multi-cluster environments via Helm charts and GitOps channels. However, security researchers discovered an authorization enforcement flaw in how the controller processes user-submitted subscriptions.

Under normal security design, deploying cluster-scoped resources requires the open-cluster-management:subscription-admin role. However, CVE-2026-10090 allows an authenticated user with basic, namespace-scoped “edit” rights in an ACM hub namespace to construct a malicious attack path:

• Channel & Subscription Creation: The attacker defines a namespaced Channel pointing to an external or attacker-controlled Helm repository and creates a Subscription resource referencing it.
• Unchecked Privileged Execution: The app-subscription controller fetches the Helm chart and executes the manifest under its own elevated cluster authority without checking if the requester possesses subscription-admin rights.
• Arbitrary ClusterRoleBinding Injection: By including a ClusterRoleBinding manifest within the Helm chart that binds the attacker’s ServiceAccount to the cluster-admin role, the controller automatically grants the attacker unrestricted, cluster-wide administrative privileges.

Compounding Multi-Cluster Risks: CVE-2026-10059

The disclosure accompanies a related vulnerability, CVE-2026-10059, affecting the ClusterCurator controller in the underlying Multicluster Engine. In a similar pattern, namespace-scoped tenant administrators can manipulate lifecycle custom resources to mint tokens for high-privilege ServiceAccounts, breaking tenant isolation in multi-tenant OpenShift clusters.

Recommended Mitigation and Containment Actions

Because these flaws allow complete compromise of confidentiality, integrity, and availability across all managed workloads and connected clusters, Red Hat and security researchers recommend immediate remediation:

• Upgrade Red Hat ACM & Multicluster Engine: Apply the latest Red Hat security errata and upgrade ACM deployment builds to vendor-patched releases immediately.
• Restrict Custom Resource RBAC Permissions: Audit hub namespace permissions and restrict create, update, and patch rights on Channel, Subscription, and ClusterCurator custom resources to trusted cluster administrators only.
• Audit ClusterRoleBindings and Token Logs: Review Kubernetes API audit logs for unexpected ClusterRoleBinding creations or ServiceAccount token minting events initiated by multicluster-operators service accounts.

Source: Red Hat Security Advisory / NVD