S3 bucket ACL allows read to any authenticated user

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Metadata

Id: 57b9893d-33b1-4419-bcea-a717ea87e139

Cloud Provider: AWS

Platform: Terraform

Severity: High

Category: Access Control

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Description

This check identifies S3 buckets that use the authenticated-read ACL, which grants read access to any authenticated AWS user, regardless of their account. This configuration creates a significant security risk as it exposes your data to all authenticated AWS users worldwide, potentially leading to unauthorized data access and information disclosure.

Secure configuration example:

resource "aws_s3_bucket" "example" {
  bucket = "my-tf-test-bucket"
  acl    = "private"
}

Insecure configuration example:

resource "aws_s3_bucket" "example" {
  bucket = "my-tf-test-bucket"
  acl    = "authenticated-read"
}

Compliant Code Examples

provider "aws" {
  region = "us-east-1"
}

terraform {
  required_providers {
    aws = {
      source = "hashicorp/aws"
      version = "4.2.0"
    }
  }
}

resource "aws_s3_bucket" "example0" {
  bucket = "my-tf-example-bucket"
}

resource "aws_s3_bucket_acl" "example_bucket_acl" {
  bucket = aws_s3_bucket.example0.id
  acl    = "private"
}

module "s3_bucket" {
  source = "terraform-aws-modules/s3-bucket/aws"
  version = "3.7.0"

  bucket = "my-s3-bucket"
  acl    = "private"

  versioning = {
    enabled = true
  }
}

provider "aws" {
  region = "us-east-1"
}

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 3.0"
    }
  }
}

resource "aws_s3_bucket" "negative1" {
  bucket = "my-tf-test-bucket"
  acl    = "private"

  tags = {
    Name        = "My bucket"
    Environment = "Dev"
  }
}

Non-Compliant Code Examples

module "s3_bucket" {
  source = "terraform-aws-modules/s3-bucket/aws"
  version = "3.7.0"

  bucket = "my-s3-bucket"
  acl    = "authenticated-read"

  versioning = {
    enabled = true
  }
}

provider "aws" {
  region = "us-east-1"
}

terraform {
  required_providers {
    aws = {
      source = "hashicorp/aws"
      version = "4.2.0"
    }
  }
}

resource "aws_s3_bucket" "example1" {
  bucket = "my-tf-example-bucket"
}

resource "aws_s3_bucket_acl" "example_bucket_acl" {
  bucket = aws_s3_bucket.example1.id
  acl    = "authenticated-read"
}

provider "aws" {
  region = "us-east-1"
}

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 3.0"
    }
  }
}

resource "aws_s3_bucket" "positive1" {
  bucket = "my-tf-test-bucket"
  acl    = "authenticated-read"

  tags = {
    Name        = "My bucket"
    Environment = "Dev"
  }
}