How to secure an AWS S3 bucket, the actual checklist
Securing an S3 bucket is six concrete steps, in order: Block Public Access, server-side encryption with a customer-managed KMS key, default object ownership set to BucketOwnerEnforced, versioning, access logging to a separate logging bucket, and a bucket policy that explicitly denies anything outside your VPC endpoint or expected principals. Skip a step and the bucket is leakable.
Why How to secure an AWS S3 bucket matters
The order matters. Block Public Access without encryption leaks data on a leaked credential. Encryption without Block Public Access leaks data publicly with the bonus that you also paid for KMS. Each step closes one failure mode; together they close the chain that turns one mistake into a breach.
Common mistakes with How to secure an AWS S3 bucket
- Doing steps 1-3 and skipping the rest because the bucket 'looks secure'.
- Encrypting with SSE-S3 instead of SSE-KMS for sensitive data.
- Putting access logs in the same bucket as the data, circular dependency on incident.
- Not testing the bucket policy with Access Analyzer before applying.