S3 Bucket with Unsecured CORS Rule

• Query id: 98a8f708-121b-455b-ae2f-da3fb59d17e1
• Query name: S3 Bucket with Unsecured CORS Rule
• Platform: Terraform
• Severity: High
• Category: Insecure Configurations
• URL: Github

Description

If the CORS (Cross-Origin Resource Sharing) rule is defined in an S3 bucket, it should be secure
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - tf file

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    = "public-read"

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

  versioning {
    enabled = false
  }

  cors_rule {
    allowed_headers = ["*"]
    allowed_methods = ["PUT", "POST"]
    allowed_origins = ["https://s3-website-test.hashicorp.com"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
   }
}

Positive test num. 2 - tf file

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

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

resource "aws_s3_bucket" "positive2" {
  bucket = "my-tf-test-bucket"
  acl    = "public-read"

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

  versioning {
    enabled = false
  }

  cors_rule {
    allowed_headers = ["*"]
    allowed_methods = ["GET", "PUT", "POST", "DELETE", "HEAD"]
    allowed_origins = ["*"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
   }
}

Positive test num. 3 - tf file

module "s3_bucket" {
  source = "terraform-aws-modules/s3-bucket/aws"
  bucket = "s3-tf-example-versioning"
  acl    = "private"
  version = "0.0.1"

  versioning = [
    {
      enabled = true
      mfa_delete = null
    },
  ]

  cors_rule = [
   {
    allowed_headers = ["*"]
    allowed_methods = ["PUT", "POST"]
    allowed_origins = ["https://s3-website-test.hashicorp.com"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
   }
  ]
}

Positive test num. 4 - tf file

module "s3_bucket" {
  source = "terraform-aws-modules/s3-bucket/aws"
  bucket = "s3-tf-example-versioning"
  acl    = "private"
  version = "0.0.1"

  versioning = [
    {
      enabled = true
      mfa_delete = null
    },
  ]

  cors_rule = [
   {
    allowed_headers = ["*"]
    allowed_methods = ["GET", "PUT", "POST", "DELETE", "HEAD"]
    allowed_origins = ["*"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
   }
  ]
}

Positive test num. 5 - tf file

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

provider "aws" {
  # Configuration options
}

resource "aws_s3_bucket" "bbb" {
  bucket = "my-tf-test-bucket"

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

resource "aws_s3_bucket_cors_configuration" "example" {
  bucket = aws_s3_bucket.bbb.bucket

  cors_rule {
    allowed_headers = ["*"]
    allowed_methods = ["GET", "PUT", "POST", "DELETE", "HEAD"]
    allowed_origins = ["*"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - tf file

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

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

resource "aws_s3_bucket" "negative1" {
  bucket = "s3-website-test.hashicorp.com"
  acl    = "public-read"

  cors_rule {
    allowed_methods = ["PUT", "POST"]
    allowed_origins = ["https://s3-website-test.hashicorp.com"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
   }
}

Negative test num. 2 - tf file

module "s3_bucket" {
  source = "terraform-aws-modules/s3-bucket/aws"
  bucket = "s3-tf-example-versioning"
  acl    = "private"
  version = "0.0.1"

  versioning = [
    {
      enabled = true
      mfa_delete = null
    },
  ]

  cors_rule = [
   {
    allowed_methods = ["PUT", "POST"]
    allowed_origins = ["https://s3-website-test.hashicorp.com"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
   }
  ]
}

Negative test num. 3 - tf file

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

provider "aws" {
  # Configuration options
}

resource "aws_s3_bucket" "b" {
  bucket = "my-tf-test-bucket"

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

resource "aws_s3_bucket_cors_configuration" "example" {
  bucket = aws_s3_bucket.b.bucket

  cors_rule {
    allowed_methods = ["PUT", "POST"]
    allowed_origins = ["https://s3-website-test.hashicorp.com"]
    expose_headers  = ["ETag"]
    max_age_seconds = 3000
  }
}