Executive brief
Google Kubernetes Engine (GKE) Multi-Cloud provides APIs to register Kubernetes clusters across AWS and Azure into Google Cloud. A missing permission check allowed attackers to register clusters into arbitrary projects without authorization. This enabled unauthorized creation of identity tokens and impersonation of service accounts in target projects, potentially allowing attackers to gain access to sensitive workloads and data across organizational boundaries.
Technical details
The vulnerability is an authorization bypass in GKE Multi-Cloud's CreateAttachedCluster, CreateAwsCluster, and CreateAzureCluster APIs due to missing project-level permission validation. An attacker with network access to these APIs could register a cluster into an arbitrary target project's Workload Identity Federation without checking whether they have permission to modify that project. Successful exploitation allows creation of Workload Identity tokens and impersonation of Kubernetes Service Accounts bound in the target project, effectively granting the attacker the privileges of those service accounts. The vulnerability requires authentication but does not require explicit target project membership. Full details and remediation guidance are available in the GKE security bulletin linked in the advisory.
Affected products
- Google GKE Multi-Cloud Prior to patch date 2026-09-02
Timeline
- 2026-09-02: disclosed