S3 Access block should block public policy

Explanation

S3 bucket policy should have block public policy to prevent users from putting a policy that enable public access.

Possible Impact

Users could put a policy that allows public access

Suggested Resolution

Prevent policies that allow public access being PUT

Insecure Example

The following example will fail the AVD-AWS-0087 check.

---
Resources:
  BadExample:
    Properties:
      AccessControl: AuthenticatedRead
    Type: AWS::S3::Bucket

Secure Example

The following example will pass the AVD-AWS-0087 check.

---
Resources:
  GoodExample:
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicAcls: true
        BlockPublicPolicy: true
        IgnorePublicAcls: true
        RestrictPublicBuckets: true
    Type: AWS::S3::Bucket


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