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Glossary Term

Google Cloud Storage (GCS)

Google’s object storage service; public buckets or broad IAM roles can expose large volumes of sensitive data.

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What it is

Google Cloud Storage (GCS) is a highly durable, globally distributed object storage service used for backups, analytics, and application hosting. Data is organized into buckets within Google Cloud projects. Buckets support multiple storage classes—Standard, Nearline, Coldline, and Archive—each optimized for different access patterns. Access control relies on Identity and Access Management (IAM) roles, Access Control Lists (ACLs), and Uniform Bucket-Level Access (UBLA) to centralize permissions. Encryption is enabled by default with Google-managed keys, while Customer-Managed Encryption Keys (CMEK) and Customer-Supplied Encryption Keys (CSEK) offer stronger control.

GCS integrates with services like BigQuery, Dataflow, and AI/ML pipelines, supports object versioning, retention policies, and logging, and can be monitored through Security Command Center and Cloud Audit Logs. However, misconfigured IAM policies or public access permissions can make entire buckets world-readable—a recurring root cause of cloud breaches.

Why it matters

GCS frequently stores production datasets, machine learning assets, and sensitive backups. When buckets or objects are inadvertently set to public, data can be indexed by search engines or harvested by attackers. Overly broad IAM roles (such as roles/storage.admin) or leaked service account keys can enable large-scale data exfiltration. Because GCS is often interconnected with other Google Cloud services, excessive permissions can lead to lateral data leakage across projects.

How to reduce risk

  • Enforce Uniform Bucket-Level Access and apply least privilege IAM roles.
  • Block public access organization-wide using Organization Policies.
  • Use CMEK or CSEK for regulated or sensitive data sets.
  • Continuously scan for public buckets with Security Command Center and automated tools.
  • Implement VPC Service Controls to prevent data exfiltration to unauthorized networks.
  • Enable object versioning, retention policies, and audit logging to preserve evidence.
  • Monitor Cloud Audit Logs for unusual API calls, cross-project access, or key usage.