Red Hat has identified a critical privilege escalation vulnerability, designated as CVE-2026-10090, within the Application Subscription controller of its Advanced Cluster Management for Kubernetes (ACM). This flaw carries a CVSS score of 9.9, indicating its severity.
The vulnerability allows users with basic namespace-scoped ‘edit’ permissions on an ACM hub to escalate their privileges to full cluster-admin rights. This escalation grants them control over the entire managed cluster fleet, posing a significant security risk.
The issue resides in the multicluster-operators-subscription component, which manages ACM’s Application Subscription feature. An attacker with edit privileges can create a Channel resource linked to a Helm repository they control and associate it with a Subscription resource. The app-subscription controller processes this request using its elevated service account authority without verifying the creator’s actual permissions. Notably, it does not check if the user holds the ‘open-cluster-management:subscription-admin’ role and fails to restrict the resources deployed to the subscription’s namespace.
Due to this oversight, an attacker can embed cluster-scoped objects within their Helm chart, such as a ClusterRoleBinding that assigns their ServiceAccount to the ‘cluster-admin’ ClusterRole. Once the controller applies the chart, the binding is created, and the attacker gains cluster administrator privileges.
Red Hat has classified this vulnerability under CWE-267, ‘Privilege Defined With Unsafe Actions,’ and documented it in Bugzilla entry 2483292. This flaw contradicts ACM’s documented security model, which asserts that non-subscription-admin users should only deploy resources within their subscription namespace.
Organizations using ACM to enforce multi-tenant separation across hub-managed clusters may inadvertently expose every managed cluster to potential takeover by any user with edit-level access to a single namespace—a permission level often granted to developers and application teams.
Given ACM’s widespread deployment in enterprise and government environments for managing fleets of OpenShift and Kubernetes clusters, successful exploitation could lead to unauthorized access to secrets, modification of workloads, or further lateral movement across all clusters registered with the hub.
Red Hat’s advisory indicates that no dedicated mitigation currently meets the company’s criteria for ease of deployment, applicability across installations, or long-term stability. The affected package is identified as rhacm2/multicluster-operators-subscription-rhel9 under Red Hat Advanced Cluster Management for Kubernetes 2, with its current state listed as ‘Affected’ and no errata issued yet.
Until an official patch is released, security teams should audit who holds namespace-scoped edit access on ACM hub namespaces, monitor Channel and Subscription resource creation for unauthorized Helm repository references, and restrict subscription-admin privileges to trusted operators. Implementing admission control policies that block cluster-scoped resources from being deployed via application subscriptions is also advisable as an interim measure.
This vulnerability underscores the importance of rigorous access controls and continuous monitoring within Kubernetes environments. Organizations must remain vigilant and proactive in addressing such security flaws to protect their infrastructure and data.
