For AI agents: A markdown version of this page is available at https://docs.datadoghq.com/security/code_security/iac_security/iac_rules/terraform-gcp-vm-serial-ports-are-enabled-for-vm-instances.md. A documentation index is available at /llms.txt.

Serial ports are enabled for VM instances

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Metadata

Id: terraform-gcp-vm-serial-ports-are-enabled-for-vm-instances

Provider: GCP

Platform: Terraform

Severity: Medium

Category: Networking and Firewall

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Description

Google Compute Engine VM instances should not have serial ports enabled. Enabling serial ports by setting the serial-port-enable metadata attribute to true (as shown below) can allow anyone with the username, project ID, SSH key, instance name, and zone to directly access the VM, increasing the risk of unauthorized access and potential compromise.

metadata = {
  serial-port-enable = true
}

To mitigate this risk, set serial-port-enable to false to ensure that serial port access is disabled and remote attackers cannot exploit this vector:

metadata = {
  serial-port-enable = false
}

Compliant Code Examples

resource "google_compute_instance" "negative1" {
  name         = "test"
  machine_type = "e2-medium"
  zone         = "us-central1-a"

  tags = ["foo", "bar"]

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }

  scratch_disk {
    interface = "SCSI"
  }

  network_interface {
    network = "default"

    access_config {
    }
  }

  metadata = {
    serial-port-enable = "FALSE"
  }

  metadata_startup_script = "echo hi > /test.txt"

  service_account {
    scopes = ["userinfo-email", "compute-ro", "storage-ro"]
  }
}

resource "google_compute_project_metadata" "negative2" {
  metadata = {
    serial-port-enable = false
  }
}

resource "google_compute_project_metadata_item" "negative3" {
  key   = "my_metadata"
  value = "my_value"
}

Non-Compliant Code Examples

resource "google_compute_instance" "positive1" {
  name         = "test"
  machine_type = "e2-medium"
  zone         = "us-central1-a"

  tags = ["foo", "bar"]

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }

  scratch_disk {
    interface = "SCSI"
  }

  network_interface {
    network = "default"

    access_config {
    }
  }

  metadata = {
    serial-port-enable = true
  }

  metadata_startup_script = "echo hi > /test.txt"

  service_account {
    scopes = ["userinfo-email", "compute-ro", "storage-ro"]
  }
}

resource "google_compute_project_metadata" "positive2" {
  metadata = {
    serial-port-enable = "TRUE"
  }
}

resource "google_compute_project_metadata_item" "positive3" {
  key   = "serial-port-enable"
  value = "TRUE"
}