S3 buckets should each define an aws_s3_bucket_public_access_block

Explanation

The “block public access” settings in S3 override individual policies that apply to a given bucket, meaning that all public access can be controlled in one central definition for that bucket. It is therefore good practice to define these settings for each bucket in order to clearly define the public access that can be allowed for it.

Possible Impact

Public access policies may be applied to sensitive data buckets

Suggested Resolution

Define a aws_s3_bucket_public_access_block for the given bucket to control public access policies

Insecure Example

The following example will fail the aws-s3-specify-public-access-block check.

resource "aws_s3_bucket" "example" {
	bucket = "example"
	acl = "private-read"
}

Secure Example

The following example will pass the aws-s3-specify-public-access-block check.

resource "aws_s3_bucket" "example" {
	bucket = "example"
	acl = "private-read"
}
  
resource "aws_s3_bucket_public_access_block" "example" {
	bucket = aws_s3_bucket.example.id
	block_public_acls   = true
	block_public_policy = true
}

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