S3 bucket allows public policy

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Metadata

Id: 1a4bc881-9f69-4d44-8c9a-d37d08f54c50

Cloud Provider: aws

Framework: Terraform

Severity: High

Category: Access Control

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Description

S3 buckets should block public policies to prevent unauthorized access to bucket contents. When the block_public_policy attribute is set to false or not defined in the aws_s3_bucket_public_access_block resource, attackers could potentially attach public policies to the bucket, exposing sensitive data to the internet. To secure your S3 bucket, ensure that block_public_policy is set to true, as shown in the following example:

resource "aws_s3_bucket_public_access_block" "example" {
  bucket = aws_s3_bucket.example.id
  block_public_acls   = true
  block_public_policy = true
  ignore_public_acls  = false
}

Compliant Code Examples

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

  bucket = "my-s3-bucket"
  acl    = "private"
  restrict_public_buckets = true
  block_public_acls = true
  block_public_policy = true

  versioning = {
    enabled = true
  }

  policy = <<POLICY
{
  "Version": "2012-10-17",
  "Id": "MYBUCKETPOLICY",
  "Statement": [
    {
      "Sid": "IPAllow",
      "Effect": "Deny",
      "Action": "s3:*",
      "Resource": "arn:aws:s3:::my_tf_test_bucket/*",
      "Condition": {
         "IpAddress": {"aws:SourceIp": "8.8.8.8/32"}
      }
    }
  ]
}
POLICY
}

resource "aws_s3_bucket" "negative1" {
  bucket = "example"
}

resource "aws_s3_bucket_public_access_block" "negative2" {
  bucket = aws_s3_bucket.example.id

  block_public_acls   = true
  block_public_policy = true
  ignore_public_acls  = false
}

Non-Compliant Code Examples

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

  bucket = "my-s3-bucket"
  acl    = "private"
  restrict_public_buckets = true
  block_public_acls = true
  block_public_policy = false

  versioning = {
    enabled = true
  }

  policy = <<POLICY
{
  "Version": "2012-10-17",
  "Id": "MYBUCKETPOLICY",
  "Statement": [
    {
      "Sid": "IPAllow",
      "Effect": "Deny",
      "Action": "s3:*",
      "Resource": "arn:aws:s3:::my_tf_test_bucket/*",
      "Condition": {
         "IpAddress": {"aws:SourceIp": "8.8.8.8/32"}
      }
    }
  ]
}
POLICY
}

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

  bucket = "my-s3-bucket"
  acl    = "private"
  restrict_public_buckets = true
  block_public_acls = true

  versioning = {
    enabled = true
  }

  policy = <<POLICY
{
  "Version": "2012-10-17",
  "Id": "MYBUCKETPOLICY",
  "Statement": [
    {
      "Sid": "IPAllow",
      "Effect": "Deny",
      "Action": "s3:*",
      "Resource": "arn:aws:s3:::my_tf_test_bucket/*",
      "Condition": {
         "IpAddress": {"aws:SourceIp": "8.8.8.8/32"}
      }
    }
  ]
}
POLICY
}

resource "aws_s3_bucket" "positive1" {
  bucket = "example"
}

resource "aws_s3_bucket_public_access_block" "positive2" {
  bucket = aws_s3_bucket.example.id

  block_public_acls   = true
  block_public_policy = false
  ignore_public_acls  = false
}

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resource "aws_s3_bucket_public_access_block" "positive3" {
  bucket = aws_s3_bucket.example.id

  block_public_acls   = true
  ignore_public_acls  = false
}