Description

A flaw was found in multicluster-global-hub. During a ManagedClusterMigration, the system incorrectly grants all managed hubs read access to a shared communication topic. This allows a compromised managed hub to intercept and collect sensitive bootstrap kubeconfigs, which contain API server tokens intended for other hubs. These tokens have an extended validity of approximately 9.86 years, significantly increasing the risk of unauthorized access and information disclosure to other managed clusters.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.3",
  "pubDate": "2026-08-10T17:17:36.197Z",
  "pubdate": "2026-08-10T17:17:36.197Z",
  "executiveSummary": "An authorization vulnerability has been identified in multicluster-global-hub concerning the ManagedClusterMigration process. The flaw manifests as an improper access control implementation where the system incorrectly provisions all managed hubs with read access to a shared communication topic. This security deficit introduces severe risk implications regarding information disclosure and unauthorized resource access across distinct management domains.\nThe primary impact of this vulnerability involves the potential interception of sensitive bootstrap kubeconfigs. These artifacts contain high-privilege API server tokens specifically intended for other managed hubs. Due to an extended token validity period of approximately 9.86 years, successful interception creates a persistent exposure window that significantly amplifies the risk profile.\nAn attacker capable of compromising a single managed hub can leverage this excessive authorization to passively or actively collect these bootstrap credentials from the shared communication channel. Exploitation requires initial compromise of a managed hub participant within the multicluster architecture, after which the vulnerability facilitates lateral reconnaissance and credential harvesting without necessitating further authentication bypasses.",
  "technicalDetails": "The root cause of the vulnerability resides in the authorization logic governing the ManagedClusterMigration workflow within multicluster-global-hub. Specifically, the component responsible for topic provisioning fails to enforce principle-of-least-privilege scoping, resulting in overly permissive Access Control Lists (ACLs) or publish-subscribe topic policies that grant read privileges globally to all connected managed hubs rather than restricting access to the designated recipient.\nThe vulnerable component is the messaging infrastructure handling inter-hub communication and migration coordination. During a ManagedClusterMigration event, bootstrap kubeconfigs—which encapsulate critical API server access tokens—are transmitted across the communication bus. Because the shared communication topic lacks proper segmentation or encryption-in-transit boundaries tied to specific tenant identities, any participant authenticated to the broker can read messages published to the shared topic.\nThe step-by-step attack flow proceeds as follows: First, an adversary achieves code execution or administrative control over a single managed hub, establishing the prerequisite attacker capabilities. Second, the adversary monitors the shared communication topic utilized during migration operations. Third, when a ManagedClusterMigration is initiated for another cluster, the central control plane publishes the bootstrap kubeconfig containing the sensitive API server tokens to the shared channel. Fourth, the compromised managed hub intercepts this payload due to its overly broad read permissions. Finally, the adversary extracts the long-lived tokens from the captured bootstrap kubeconfigs.\nThe post-exploitation impact is severe due to the longevity of the compromised credentials. The harvested API server tokens possess an extended validity period of approximately 9.86 years. This grants the attacker persistent, unauthorized access to API servers and managed clusters intended strictly for other administrative hubs, bypassing standard rotation policies and enabling long-term unauthorized cluster manipulation, data exfiltration, and lateral movement across the enterprise multicluster environment."
}