Network ACL With Unrestricted Access To SSH

• Query id: 3af7f2fd-06e6-4dab-b996-2912bea19ba4
• Query name: Network ACL With Unrestricted Access To SSH
• Platform: Terraform
• Severity: Medium
• Category: Networking and Firewall
• CWE: 668
• URL: Github

Description

'SSH' (TCP:22) should not be public in AWS Network ACL
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_network_acl" "positive1" {
  vpc_id = aws_vpc.main.id

  egress = [
    {
      protocol   = "tcp"
      rule_no    = 200
      action     = "allow"
      cidr_block = "10.3.0.0/18"
      from_port  = 443
      to_port    = 443
    }
  ]

  ingress = [
    {
      protocol   = "tcp"
      rule_no    = 100
      action     = "allow"
      cidr_block = "0.0.0.0/0"
      from_port   = 22
      to_port     = 22
    }
  ]

  tags = {
    Name = "main"
  }
}

Positive test num. 2 - tf file

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

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

resource "aws_network_acl" "positive2" {
  vpc_id = aws_vpc.main.id

  tags = {
    Name = "main"
  }
}

resource "aws_network_acl_rule" "postive2" {
  network_acl_id = aws_network_acl.positive2.id
  rule_number    = 100
  egress         = false
  protocol       = "tcp"
  rule_action    = "allow"
  from_port      = 22
  to_port        = 22
  cidr_block     = "0.0.0.0/0"
}

Positive test num. 3 - tf file

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

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "<= 3.52.0"
    }
  }
}

resource "aws_network_acl" "positive3" {
  vpc_id = aws_vpc.main.id

  egress {
      protocol   = "tcp"
      rule_no    = 200
      action     = "allow"
      cidr_block = "10.3.0.0/18"
      from_port  = 443
      to_port    = 443
  }

  ingress {
      protocol   = "tcp"
      rule_no    = 100
      action     = "allow"
      cidr_block = "0.0.0.0/0"
      from_port   = 22
      to_port     = 22
  }

  tags = {
    Name = "main"
  }
}

Positive test num. 4 - tf file

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"]

  default_network_acl_ingress = [
    {
      "action" : "allow",
      "cidr_block" : "0.0.0.0/0",
      "from_port" : 0,
      "protocol" : "tcp",
      "rule_no" : 22,
      "to_port" : 0
    }
  ]

  enable_nat_gateway = true
  enable_vpn_gateway = true

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

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_network_acl" "negative1" {
  vpc_id = aws_vpc.main.id

  egress = [
    {
      protocol   = "tcp"
      rule_no    = 200
      action     = "allow"
      cidr_block = "10.3.0.0/18"
      from_port  = 443
      to_port    = 443
    }
  ]

  ingress = [
    {
      protocol   = "tcp"
      rule_no    = 100
      action     = "allow"
      cidr_block = "10.3.0.0/18"
      from_port   = 22
      to_port     = 22
    }
  ]

  tags = {
    Name = "main"
  }
}

Negative test num. 2 - tf file

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

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

resource "aws_network_acl" "negative2" {
  vpc_id = aws_vpc.main.id

  tags = {
    Name = "main"
  }
}

resource "aws_network_acl_rule" "negative2" {
  network_acl_id = aws_network_acl.positive1.id
  rule_number    = 100
  egress         = false
  protocol       = "tcp"
  rule_action    = "allow"
  from_port      = 22
  to_port        = 22
  cidr_block     = "10.3.0.0/18"
}

Negative test num. 3 - tf file

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

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "3.52.0"
    }
  }
}

resource "aws_network_acl" "negative3" {
  vpc_id = aws_vpc.main.id

  egress {
      protocol   = "tcp"
      rule_no    = 200
      action     = "allow"
      cidr_block = "10.3.0.0/18"
      from_port  = 443
      to_port    = 443
  }

  ingress {
      protocol   = "tcp"
      rule_no    = 100
      action     = "allow"
      cidr_block = "10.3.0.0/18"
      from_port   = 22
      to_port     = 22
  }

  tags = {
    Name = "main"
  }
}

Negative test num. 4 - tf file

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"
  }
}

Negative test num. 5 - tf file

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"]

  default_network_acl_ingress = [
    {
      "action" : "allow",
      "cidr_block" : "0.0.0.0/0",
      "from_port" : 0,
      "protocol" : "-1",
      "rule_no" : 100,
      "to_port" : 0
    },
    {
      "action" : "allow",
      "cidr_block" : "10.3.0.0/18",
      "from_port" : 0,
      "protocol" : "-1",
      "rule_no" : 22,
      "to_port" : 0
    }
  ]

  enable_nat_gateway = true
  enable_vpn_gateway = true

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