GCP Cloud Storage Hardening: Blocking Public Exposures

Google Cloud Storage (GCS) buckets are the primary file storage vault for modern SaaS startups. However, if database backups or client PDFs are exposed publicly, crawlers can index them.

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How Exposure Gaps Occur

Bucket exposures occur when administrators use legacy Access Control Lists (ACLs) that conflict with project-level IAM roles, or accidentally add the member identifier allUsers or allAuthenticatedUsers with the role Storage Object Viewer.

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Remediation Steps

1. Enforce Uniform Bucket-Level Access

Disable legacy ACLs. Enforce uniform bucket-level access controls so IAM is the single authority for resource access:

gcloud storage buckets update gs://private-bucket-name --uniform-bucket-level-access

2. Implement GCP Public Access Prevention (PAP)

Enable Public Access Prevention on the target buckets to enforce a project-wide block on public sharing:

gcloud storage buckets update gs://private-bucket-name --public-access-prevention=enforced

3. Implement Pre-signed URLs

If files must be shared with users, generate short-lived signed URLs with 15-minute expiration times.