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Ensure that S3 Buckets are configured with 'Block public access (bucket settings)'

Amazon S3 provides Block public access (bucket settings) and Block public access (account settings) to help you manage public access to Amazon S3 resources. By default, S3 buckets and objects are created with public access disabled. However, an IAM principal with sufficient S3 permissions can enable public access at the bucket and/or object level. While enabled, Block public access (bucket settings) prevents an individual bucket, and its contained objects, from becoming publicly accessible. Similarly, Block public access (account settings) prevents all buckets, and contained objects, from becoming publicly accessible across the entire account.

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Risk Level: Critical
Cloud Entity: Simple Storage Service (S3)
CloudGuard Rule ID: D9.AWS.NET.72
Covered by Spectral: Yes
Category: Storage

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S3Bucket should have (accessPublicBlock.blockPublicAcls=true or accountAccessPublicBlock.blockPublicAcls=true) and (accessPublicBlock.ignorePublicAcls=true or accountAccessPublicBlock.ignorePublicAcls=true) and (accessPublicBlock.blockPublicPolicy=true or accountAccessPublicBlock.blockPublicPolicy=true) and (accessPublicBlock.restrictPublicBuckets=true or accountAccessPublicBlock.restrictPublicBuckets=true)

REMEDIATION

From Console

  1. Login to AWS Management Console and open the Amazon S3 console using https://console.aws.amazon.com/s3/
  2. Select the Check box next to the Bucket
  3. Click on 'Edit public access settings'
  4. Click 'Block all public access'
  5. Repeat for all the buckets in your AWS account that contain sensitive data

From TF
To enable block public access bucket setting, add following in a terraform file:

resource "aws_s3_bucket_public_access_block" "public_access_block_example" {
	bucket = BUCKET-NAME
	block_public_acls = true
	block_public_policy = true
	restrict_public_buckets = true
	ignore_public_acls = true
}

From Command Line
To set Block Public Access configurations, run:

aws s3api put-public-access-block --bucket BUCKET_NAME --public-access-block-configuration "BlockPublicAcls=true,IgnorePublicAcls=true,BlockPublicPolicy=true,RestrictPublicBuckets=true"

References

  1. https://docs.aws.amazon.com/AmazonS3/latest/dev/access-control-block-public-access.html#console-block-public-access-options
  2. https://docs.aws.amazon.com/AmazonS3/latest/user-guide/block-public-access-bucket.html
  3. https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/s3_account_public_access_block
  4. https://awscli.amazonaws.com/v2/documentation/api/latest/reference/s3api/put-public-access-block.html

Simple Storage Service (S3)

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Updated over 1 year ago