Instances should use a non-default service account

google_compute_instance

Description

To follow the principle of least privileges and to prevent potential privilege escalation, assign instances to a service account other than the default Compute Engine service account.

Rationale

Even when used with the default “Allow default access” scope, the default Compute Engine service account has sensitive read permissions. For instance, it can access data from all Google Cloud Storage buckets in the project.

To defend against data theft if your VM is compromised and prevent an attacker from gaining access to sensitive data in your project, it is recommended that you not use the default Compute Engine service account. Instead, create a new service account and assign only the permissions needed by your instance.

The default Compute Engine service account is named [PROJECT_NUMBER]-compute@developer.gserviceaccount.com.

Exception

VMs created by GKE are excluded from this guidance. These VMs have names that start with gke- and are labeled goog-gke-node.

Remediation

From the console

  1. Go to the VM instances page by visiting: https://console.cloud.google.com/compute/instances.
  2. Click on the instance name to go to its VM instance details page.
  3. Click STOP and then click EDIT.
  4. Under the section API and identity management, select a service account other than the default Compute Engine service account. You may first need to create a new service account.
  5. Click Save and then click START.

From the command line

  1. Stop the instance:
    gcloud compute instances stop <INSTANCE_NAME>
  2. Update the instance:
    gcloud compute instances set-service-account <INSTANCE_NAME> --service-account=<SERVICE_ACCOUNT>
  3. Restart the instance:
    gcloud compute instances start <INSTANCE_NAME>

Default value

By default, Compute instances are configured to use the default Compute Engine service account.

References

  1. https://cloud.google.com/compute/docs/access/service-accounts#default_service_account
  2. https://cloud.google.com/compute/docs/access/service-accounts#accesscopesiam
  3. https://cloud.google.com/compute/docs/access/service-accounts
  4. [https://cloud.google.com/compute/docs/access/create-enable-service-accounts-for-instances][5]
  5. [https://cloud.google.com/sdk/gcloud/reference/compute/instances/set-service-account][6]

CIS Controls

Version 8 - 4.7: Manage Default Accounts on Enterprise Assets and Software

  • Manage default accounts on enterprise assets and software, such as root, administrator, and other pre-configured vendor accounts. Example implementations can include: disabling default accounts or making them unusable.

Version 7 - 4.7 Limit Access to Script Tools

  • Limit access to scripting tools (such as Microsoft PowerShell and Python) to only administrative or development users with the need to access those capabilities.