Default VPC exists

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Metadata

Id: 96ed3526-0179-4c73-b1b2-372fde2e0d13

Cloud Provider: aws

Framework: Terraform

Severity: Medium

Category: Insecure Defaults

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Description

Using the default VPC in AWS is not recommended, as it is a shared environment with default configurations that may not align with an organization’s security and networking requirements. Resources created in the default VPC are more susceptible to unintended access, misconfiguration, or exposure. To mitigate this risk, it is best to define a custom VPC, as in the following example:

resource "aws_vpc" "main" {
  cidr_block       = "10.0.0.0/16"
  instance_tenancy = "default"

  tags = {
    Name = "main"
  }
}

This ensures network isolation and enables more granular control over security settings.

Compliant Code Examples

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "3.7.0"

  name = "my-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  enable_nat_gateway = true
  enable_vpn_gateway = true

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

resource "aws_vpc" "negative1" {
  cidr_block       = "10.0.0.0/16"
  instance_tenancy = "default"

  tags = {
    Name = "main"
  }
}

Non-Compliant Code Examples

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "3.7.0"

  name = "my-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  enable_nat_gateway = true
  enable_vpn_gateway = true
  default_vpc_name   = "my-default-vpc"

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

resource "aws_default_vpc" "positive1" {
  tags = {
    Name = "Default VPC"
  }
}