IP forwarding enabled

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Metadata

Id: f34c0c25-47b4-41eb-9c79-249b4dd47b89

Cloud Provider: GCP

Platform: Terraform

Severity: Medium

Category: Networking and Firewall

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Description

This check ensures that the can_ip_forward attribute for Google Compute Engine instances is set to false, which prevents instances from forwarding packets not addressed to them. If can_ip_forward is set to true, as shown below, the instance could be misused as a routing or proxy device, increasing the risk of data exfiltration or man-in-the-middle attacks:

resource "google_compute_instance" "appserver" {
  name           = "primary-application-server"
  machine_type   = "e2-medium"
  can_ip_forward = true
  ...
}

To mitigate this risk, configure the attribute as false:

resource "google_compute_instance" "appserver" {
  name           = "primary-application-server"
  machine_type   = "e2-medium"
  can_ip_forward = false
  ...
}

Disabling IP forwarding hardens network boundaries and reduces the attack surface of the cloud environment.

Compliant Code Examples

resource "google_compute_instance" "appserver" {
  name           = "primary-application-server"
  machine_type   = "e2-medium"
  can_ip_forward = false

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-11"
    }
  }

  network_interface {
    network = "default"
  }
}

Non-Compliant Code Examples

resource "google_compute_instance" "appserver" {
  name           = "primary-application-server"
  machine_type   = "e2-medium"
  can_ip_forward = true

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-11"
    }
  }

  network_interface {
    network = "default"
  }
}