The rule 'GCP GCS IAM Permission Changes' is designed to monitor changes made to the Identity and Access Management (IAM) permissions of Google Cloud Storage (GCS) buckets. By detecting permission modifications promptly, organizations can reduce the risk of unauthorized access to sensitive data stored in GCS. The rule listens for relevant log events from GCP's Audit Logs, particularly focusing on activities that might alter IAM policies such as 'storage.setIamPermissions'. The expected outcome is a log entry that matches predefined criteria, confirming that a permission change has occurred. The rule has a low severity, indicating that while important, it may not require immediate action unless the changes are deemed suspicious. The runbook advises verifying the legitimacy of the detected bucket permission changes. The inclusion of the CIS compliance requirement highlights its relevance in meeting security standards. The rule utilizes audit logging to ensure a thorough tracking of who made changes, when, and what specifically was altered.