Security group with unrestricted access to SSH

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Metadata

Id: 65905cec-d691-4320-b320-2000436cb696

Cloud Provider: AWS

Platform: Terraform

Severity: Medium

Category: Networking and Firewall

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Description

This check verifies that AWS security groups do not allow unrestricted inbound access to port 22 (SSH) from the public internet (cidr_blocks = ["0.0.0.0/0"]). Allowing public SSH access exposes instances to unauthorized access attempts and automated attacks, increasing the risk of successful brute-force compromises. To mitigate this vulnerability, the cidr_blocks attribute in the ingress block should be restricted to trusted IP ranges only, as shown below:

Insecure configuration:

ingress {
  from_port   = 22
  to_port     = 22
  protocol    = "tcp"
  cidr_blocks = ["0.0.0.0/0"]
}

Secure configuration:

ingress {
  from_port   = 22
  to_port     = 22
  protocol    = "tcp"
  cidr_blocks = ["192.120.0.0/16", "75.132.0.0/16"]
}

If left unaddressed, this misconfiguration can lead to remote attackers gaining entry to instances via SSH, putting sensitive data and critical infrastructure at risk.

Compliant Code Examples

module "vote_service_sg" {
  source = "terraform-aws-modules/security-group/aws"
  version = "4.3.0"
  name        = "user-service"
  description = "Security group for user-service with custom ports open within VPC, and PostgreSQL publicly open"
  vpc_id      = "vpc-12345678"

  ingress {
    description = "TLS from VPC"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["192.120.0.0/16", "75.132.0.0/16"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "allow_tls"
  }
}


resource "aws_security_group" "negative1" {
  name        = "allow_tls"
  description = "Allow TLS inbound traffic"
  vpc_id      = aws_vpc.main.id

  ingress {
    description = "TLS from VPC"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["192.120.0.0/16", "75.132.0.0/16"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "allow_tls"
  }
}

Non-Compliant Code Examples

resource "aws_security_group" "positive2" {
  name        = "allow_tls"
  description = "Allow TLS inbound traffic"
  vpc_id      = aws_vpc.main.id

  ingress {
    description = "TLS from VPC"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["192.120.0.0/16", "0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "allow_tls"
  }
}

module "vote_service_sg" {
  source = "terraform-aws-modules/security-group/aws"
  version = "4.3.0"
  name        = "user-service"
  description = "Security group for user-service with custom ports open within VPC, and PostgreSQL publicly open"
  vpc_id      = "vpc-12345678"

  ingress {
    description = "TLS from VPC"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "allow_tls"
  }
}

module "vote_service_sg" {
  source = "terraform-aws-modules/security-group/aws"
  version = "4.3.0"
  name        = "user-service"
  description = "Security group for user-service with custom ports open within VPC, and PostgreSQL publicly open"
  vpc_id      = "vpc-12345678"

  ingress {
    description = "TLS from VPC"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["192.120.0.0/16", "0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "allow_tls"
  }
}