Define Allowed External IPs for VM Instances

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Risk level: Medium (should be achieved)

Ensure that "Define Allowed External IPs for VM Instances" constraint policy is enforced at the GCP organization level in order to enable you to define the set of virtual machine (VM) instances that are allowed to use external IP addresses. This constraint helps you to minimize your instance's exposure to the Internet. The allowed list of VM instances must be identified by the instance name, using the following format: projects/<project-id>/zones/<instance-zone>/instances/<instance-name> and must be defined in the conformity rule settings, on the Trend Micro Cloud One™ – Conformity account console.

Security

By default, all Google Cloud virtual machine instances are allowed to use external IP addresses. To reduce the attack surface, not all virtual machine instances should have public IP addresses attached.

Note: To avoid breaking existing cloud infrastructure, you should test this constraint policy on non-production projects and folders within your organization.


Audit

To determine if "Define Allowed External IPs for VM Instances" constraint policy is enabled for your GCP organizations, perform the following actions:

Using GCP Console

01 Sign in to Google Cloud Management Console with the organizational unit credentials.

02 Click on the deployment selector from the top navigation bar, select ALL to list all the existing deployments, then choose the Google Cloud organization that you want to examine.

03 Navigate to Cloud Identity and Access Management (IAM) dashboard at https://console.cloud.google.com/iam-admin/iam.

04 In the navigation panel, select Organization Policies to access the complete list of the constraint policies available for your GCP organization.

05 Click inside the Filter by policy name or ID filter box, select Name and Define allowed external IPs for VM instances to return the "Define Allowed External IPs for VM Instances" policy.

06 Click on the name of the GCP organization policy returned at the previous step.

07 On the Policy details page, under Effective policy, check the Allowed configuration attribute value. If the Allowed attribute value is set to All, the policy constraints are not enforced in your organization, therefore all the virtual machine instances created within the selected Google Cloud Platform (GCP) organization are allowed to use external IP addresses.

08 Repeat steps no. 2 – 7 for each organization available in your Google Cloud account.

Using GCP CLI

01 Run organizations list command (Windows/macOS/Linux) using custom query filters to list the ID of each organization available within your Google Cloud account:

gcloud organizations list
    --format="table(name)"

02 The command output should return the requested organization identifiers (IDs):

ID
112233441122
123412341234

03 Run resource-manager org-policies describe command (Windows/macOS/Linux) using the ID of the GCP organization that you want to examine as identifier parameter, to describe the enforcement configuration of the "Define Allowed External IPs for VM Instances" policy, available for the selected GCP organization:

gcloud alpha resource-manager org-policies describe
"compute.vmExternalIpAccess"
    --effective
    --organization=112233441122
    --format="value(listPolicy.allValues)"

04 The command request should return the requested configuration information:

ALLOW

If the resource-manager org-policies describe command output returns ALLOW, as shown in the example above, the "Define Allowed External IPs for VM Instances" policy constraints are not enforced within your organization, therefore all the virtual machine instances deployed within the selected Google Cloud Platform (GCP) organization are allowed to use external IP addresses.

05 Repeat step no. 3 and 4 for each organization created within your Google Cloud account.

Remediation / Resolution

To minimize your Google Cloud virtual machine instances exposure to the Internet, enable and configure the "Define Allowed External IPs for VM Instances" policy at the GCP organization level by performing the following actions:

Using GCP Console

01 Sign in to your Trend Micro Cloud One™ – Conformity account, access Define Allowed External IPs for VM Instances conformity rule settings and note the list of virtual machine instances that are allowed to use external IP addresses, available within your GCP organization.

02 Sign in to Google Cloud Management Console with the organizational unit credentials.

03 Click on the deployment selector from the top navigation bar, select ALL to list all the existing deployments, then choose the Google Cloud organization that you want to reconfigure.

04 Navigate to Cloud Identity and Access Management (IAM) dashboard at https://console.cloud.google.com/iam-admin/iam.

05 In the navigation panel, select Organization Policies to access the list with the cloud organization policies available for your organization.

06 Click inside the Filter by policy name or ID filter box, select Name and Define allowed external IPs for VM instances to list only the "Define Allowed External IPs for VM Instances" policy.

07 Click on the name of the GCP organization policy returned at the previous step.

08 On the Policy details page, click on the EDIT button from the dashboard top menu to edit the selected policy.

09 On the Edit policy configuration page, perform the following operations:

  1. Under Applies to, select Customize to choose the type of the policy to apply (i.e. customized policy).
  2. To override the inherited policies completely, select Replace under Policy enforcement.
  3. To use explicit values, select Custom from the Policy values dropdown list.
  4. For Policy type, select Allow to specify that the listed values will be the only allowed values, and all other values will be denied.
  5. In the Custom values section, use the configuration controls to define the Compute Engine virtual machine instances that are allowed to use external IP addresses within your GCP organization, identified at step no. 1. Use the following format to define the allowed VM instances: projects/<ect-id>/zones/<instance-zone>/instances/<instance-name>ere <project-id>the ID of the instance's project, the <instance-zone> is the Google Cloud zone where the instance was deployed, and the <instance-name> is the name of the VM instance allowed to use external IPs.
  6. (Optional) To set a recommendation for other users, click SET RECOMMENDATION, enter a string value into the Recommended value text box, and click SET to apply the recommendation. This string value will be displayed in the Google Cloud console to provide guidance to users about this organization policy. This is just a communication tool, and does not affect the policy configuration.
  7. Click SAVE to apply the changes and enforce the "Define Allowed External IPs for VM Instances" policy constraints.

10 If required, repeat steps no. 3 – 9 to enable the required policy for other organizations available in your Google Cloud account.

Using GCP CLI

01 Sign in to your Trend Micro Cloud One™ – Conformity account, access Define Allowed External IPs for VM Instances conformity rule settings and note the list of virtual machine instances that are allowed to use external IP addresses, provisioned within your GCP organization.

02 Configure the "Define Allowed External IPs for VM Instances" policy constraints and save the YAML policy document to a file named cc-allowed-vm-instances-policy.yaml. Use the list of allowed Google Cloud VM instances identified at step no. 1 to configure the allowed_values list. The following organization policy example allows using external IPs for a VM instance identified by projects/<project-id>/zones/<instance-zone>/instances/<instance-name>, where <project-id> is the ID of the instance's project, the <instance-zone> is the Google Cloud zone where the instance was provisioned, and the <instance-name> is the name of the VM instance allowed to use external IPs (e.g. projects/cc-project5/zones/us-central1-a/instances/cc-frontend-vm-instance):

constraint: constraints/compute.vmExternalIpAccess
listPolicy:
  allowed_values:
    projects/cc-project5/zones/us-central1-a/instances/cc-frontend-vm-instance

03 Run resource-manager org-policies set-policy command (Windows/macOS/Linux) using the ID of the Google Cloud Platform (GCP) organization that you want to reconfigure as identifier parameter, to enforce the "Define Allowed External IPs for VM Instances" policy (i.e. "compute.vmExternalIpAccess" constraint), using the policy document defined at the previous step, for the selected organization:

gcloud beta resource-manager org-policies set-policy cc-allowed-vm-instances-policy.yaml
    --organization=112233441122

04 The command request should return the enforced organization policy metadata:

constraint: constraints/compute.vmExternalIpAccess
etag: abcdabcdabcd
listPolicy:
  allowedValues:
  - projects/cc-project5/zones/us-central1-a/instances/cc-frontend-vm-instance
updateTime: '2020-09-03T00:00:00.000Z'

05 If required, repeat step no. 3 and 4 to enforce the necessary policy for other organizations created within your Google Cloud account.

References

Publication date May 10, 2021

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Define Allowed External IPs for VM Instances

Risk level: Medium