Since the cloud storage buckets were meant to be accessible by a specific department only but are publicly accessible, it is likely that the access policies for the storage buckets were misconfigured. The correct configuration should have set the permissions to allow only the specific department access, not the general public. An expired SSL/TLS certificate would affect secure communication, but not the access policy of the storage buckets. Network ACLs and security groups are more related to network traffic control rather than defining access policies for storage buckets.