CVE-2026-66793

A flaw was found in the Application Subscription controller (multicluster-operators-subscription) of Red Hat Advanced Cluster Management for Kubernetes (ACM). A user with namespace-scoped "edit" privileges in an ACM hub namespace can create a Channel resource pointing to a Helm repository they control and a Subscription resource referencing it. The app-subscription controller fetches and applies the Helm chart contents with its own elevated authority, without verifying whether the subscription creator holds the "open-cluster-management:subscription-admin" role and without restricting applied resources to the subscription namespace. This allows the attacker to include cluster-scoped resources in the Helm chart, such as a ClusterRoleBinding granting the attacker's ServiceAccount the "cluster-admin" ClusterRole. Successful exploitation results in full cluster-admin privilege escalation.

A flaw in the lighthouse component of Red Hat Advanced Cluster Management for Kubernetes stems from insufficient validation of advertised IP addresses in EndpointSlice objects. A compromised spoke cluster can create EndpointSlices with attacker-controlled IPs, causing other clusters' lighthouse DNS to redirect legitimate service traffic to malicious endpoints, enabling Man-in-the-Middle attacks.

In the must-gather component of Red Hat Advanced Cluster Management for Kubernetes, the cluster Proxy object is dumped in raw form, bypassing the oc inspect redaction that would normally sanitize sensitive fields. This exposes proxy basic-auth credentials in the must-gather archive, potentially disclosing sensitive authentication information to anyone with access to the archive.

In the must-gather component of Red Hat Advanced Cluster Management for Kubernetes, certain ACM wrapper Custom Resources that embed Secret data are collected without redaction. When an administrator runs must-gather, credentials and tokens are captured in cleartext in the resulting archive, potentially exposing sensitive information to anyone with access to the archive.

In the service-proxy component of Red Hat Advanced Cluster Management for Kubernetes (RHACM) and multicluster-engine (MCE), the proxy appends impersonation headers without removing caller-supplied values. An authenticated hub principal can inject an Impersonate-Group header to escalate to cluster-admin on every managed cluster.