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Description

Compute instances should not be configured to have external IP addresses.

Rationale​

To reduce your attack surface, Compute instances should not have public IP addresses. Instead, instances should be configured behind load balancers, to minimize the instance's exposure to the internet.

Impact​

Removing the external IP address from your Compute instance may cause some applications to stop working.

Audit​

From Google Cloud Console​

  1. Go to the VM instances page by visiting: https://console.cloud.google.com/compute/instances.
  2. For every VM, ensure that there is no External IP configured.

From Google Cloud CLI​

        gcloud compute instances list --format=json

  1. The output should not contain an accessConfigs section under networkInterfaces. Note that the natIP value is present only for instances that are running or for instances that are stopped but have a static IP address. For instances that are stopped and are configured to have an ephemeral public IP address, the natIP field will not be present. Example output:

         networkInterfaces: 
         - accessConfigs: 
             - kind: compute#accessConfig 
               name: External NAT 
               networkTier: STANDARD 
               type: ONE_TO_ONE_NAT

Exception​

Instances created by GKE should be excluded because some of them have external IP addresses and cannot be changed by editing the instance settings. Instances created by GKE should be excluded. These instances have names that start with gke- and are labeled goog-gke-node.

Prevention​

You can configure the Define allowed external IPs for VM instances Organization Policy to prevent VMs from being configured with public IP addresses. Learn more at: https://console.cloud.google.com/orgpolicies/compute-vmExternalIpAccess

Default Value​

By default, Compute instances have a public IP address.

References​

  1. https://cloud.google.com/load-balancing/docs/backend-service#backends_and_external_ip_addresses
  2. https://cloud.google.com/compute/docs/instances/connecting-advanced#sshbetweeninstances
  3. https://cloud.google.com/compute/docs/instances/connecting-to-instance
  4. https://cloud.google.com/compute/docs/ip-addresses/reserve-static-external-ip-address#unassign_ip
  5. https://cloud.google.com/resource-manager/docs/organization-policy/org-policy-constraints

Additional Information​

You can connect to Linux VMs that do not have public IP addresses by using Identity-Aware Proxy for TCP forwarding. Learn more at https://cloud.google.com/compute/docs/instances/connecting-advanced#sshbetweeninstances

For Windows VMs, see https://cloud.google.com/compute/docs/instances/connecting-to-instance.