Red Hat has disclosed a critical privilege-escalation vulnerability in Red Hat Advanced Cluster Management for Kubernetes (ACM) that could allow a user with limited namespace-level editing permissions to obtain full cluster-admin access across a Kubernetes environment.
Tracked as CVE-2026-10090, the vulnerability affects the Application Subscription controller, also known as multicluster-operators-subscription.
Red Hat assigned the issue an Important severity rating and a CVSS v3.1 score of 9.9 out of 10. The flaw was made public on August 5, 2026.
Red Hat ACM Flaw
The issue is especially significant because it violates a core Kubernetes authorization boundary: the separation between permissions granted within a namespace and permissions that apply across the entire cluster.
In a vulnerable ACM hub, an attacker does not need pre-existing cluster-wide administrative rights. Namespace-scoped edit access in an ACM hub namespace is sufficient.
The vulnerable workflow involves ACM’s Channel and Subscription custom resources. A user with namespace-level edit privileges can create a Channel resource that points to a Helm repository under their control.
They can then create a Subscription resource referencing that Channel. The Application Subscription controller retrieves the Helm chart and applies its content using the controller’s own elevated permissions.
Crucially, Red Hat said the controller does not verify whether the user who created the Subscription holds the required open-cluster-management:subscription-admin role.
It also fails to constrain the resources deployed from the Helm chart to the namespace in which the Subscription was created. As a result, a chart supplied by an attacker can contain cluster-scoped Kubernetes objects.
One high-impact example is a ClusterRoleBinding that binds an attacker-controlled ServiceAccount to Kubernetes’ built-in cluster-admin ClusterRole. Once applied by the privileged controller, that binding gives the attacker unrestricted control over the entire cluster.
The attack requires low privileges, low complexity, and no user interaction. Red Hat’s CVSS vector reflects the broad consequences of successful exploitation: network reachability, low privileges required, changed scope.
The vulnerability contradicts ACM’s documented security model. Red Hat documentation states that users who are not subscription administrators should have application resources deployed only into the Subscription namespace.
CVE-2026-10090 effectively bypasses that expectation by allowing a limited editor to cause a highly privileged controller to deploy arbitrary cluster-scoped objects.
For organizations that use ACM to manage applications across multiple Kubernetes clusters, a compromise of the hub can be particularly damaging.
An attacker with cluster-admin on the hub could alter workloads, access secrets, establish persistence through controllers or admission resources, modify identity bindings, and potentially affect managed-cluster operations depending on the environment.
The associated weakness is classified as CWE-267, an access-control issue involving the ability to gain privileges or assume an identity.
Affected Component and Response
Red Hat lists rhacm2/multicluster-operators-subscription-rhel9 in Red Hat Advanced Cluster Management for Kubernetes 2 as affected. At the time of disclosure, no security errata had been issued.
Organizations should therefore treat this as a high-priority exposure and monitor Red Hat’s advisory and errata channels for a fixed release.
Until an update is available, defenders should tightly restrict namespace edit permissions in ACM hub namespaces, review who can create or modify Channel and Subscription resources, and audit for unexpected cluster-scoped objects.
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