S3 bucket cross-account permissions should be restricted¶

This control checks whether the S3 bucket policy prevents principals from other AWS accounts from performing denied actions on resources in the S3 bucket.

How to fix¶

Attribute policy of aws_s3_bucket_policy must contain: "StringNotEquals", "aws:PrincipalAccount".

Implementation options¶

Choose the option that matches how you manage Terraform. All options satisfy this control.

Option 1: Compliance.tf module (recommended)¶

Use the compliance.tf registry module to get this control enforced by default. This control is mapped to the frameworks shown in the tabs above. To begin, see get started with compliance.tf.

module "s3_bucket" {
  source  = "acscessentialeight.compliance.tf/terraform-aws-modules/s3-bucket/aws"
  version = ">=5.0.0"

  bucket = "abc123"
}

module "s3_bucket" {
  source  = "nistcsfv11.compliance.tf/terraform-aws-modules/s3-bucket/aws"
  version = ">=5.0.0"

  bucket = "abc123"
}

module "s3_bucket" {
  source  = "nistcsf.compliance.tf/terraform-aws-modules/s3-bucket/aws"
  version = ">=5.0.0"

  bucket = "abc123"
}

module "s3_bucket" {
  source  = "pcidss.compliance.tf/terraform-aws-modules/s3-bucket/aws"
  version = ">=5.0.0"

  bucket = "abc123"
}

Option 2: Open source module (terraform-aws-modules)¶

If you use terraform-aws-modules/s3-bucket/aws, configure the required module inputs to satisfy this control. You can later migrate to the compliance.tf module with minimal changes because it is compatible by design.

module "s3_bucket" {
  source  = "terraform-aws-modules/s3-bucket/aws"
  version = ">=5.0.0"

  bucket = "abc123"
}

Option 3: Terraform AWS provider resources¶

If you manage resources directly, configure the relevant Terraform AWS provider resources to meet this control. See docs for the resources involved: aws_s3_bucket_policy.

resource "aws_s3_bucket" "this" {
  bucket        = "example-abc123"
  force_destroy = true
}

resource "aws_s3_bucket_policy" "this" {
  bucket = "example-bucket-abc123"
  policy = jsonencode({ Version = "2012-10-17", Statement = [{ Effect = "Deny", Principal = "*", Action = "s3:*", Resource = ["arn:aws:s3:::example-bucket-abc123", "arn:aws:s3:::example-bucket-abc123/*"], Condition = { Bool = { "aws:SecureTransport" = "false" } } }] })
}

Tool mappings¶

Use these identifiers to cross-reference this control across tools, reports, and evidence.

• Compliance.tf (CTF) Control: s3_bucket_policy_restricts_cross_account_permission_changes

• Powerpipe Control: aws_compliance.control.s3_bucket_policy_restricts_cross_account_permission_changes