Description

It is recommended that IAM policies on Cloud KMS cryptokeys restrict anonymous or public access.

Rationale

Granting permissions to allUsers or allAuthenticatedUsers allows anyone to access the cryptokey. Such access might not be desirable if sensitive data is protected with that key. In this case, ensure that anonymous or public access to a Cloud KMS cryptokey is not allowed.

Impact

Removing the binding for allUsers and allAuthenticatedUsers members denies access to cryptokeys for anonymous or public users.

Audit

From Google Cloud CLI

1. List all Cloud KMS cryptokeys.

   gcloud kms keys list \
       --keyring={{key-ring-name}} \
       --location=global \
       --format=json | jq '.[].name'

2. Ensure the below command's output does not contain allUsers or allAuthenticatedUsers.

   gcloud kms keys get-iam-policy {{key-name}} \
       --keyring={{key-ring-name}} \
       --location=global \
       --format=json | jq '.bindings[].members[]'

Default Value

By default Cloud KMS does not allow access to allUsers or allAuthenticatedUsers.

References

1. https://cloud.google.com/sdk/gcloud/reference/kms/keys/remove-iam-policy-binding
2. https://cloud.google.com/sdk/gcloud/reference/kms/keys/set-iam-policy
3. https://cloud.google.com/sdk/gcloud/reference/kms/keys/get-iam-policy
4. https://cloud.google.com/kms/docs/object-hierarchy#key_resource_id

Additional Information

[key_ring_name] : is the resource ID of the key ring. This value is case-sensitive and in the form:

projects/PROJECT_ID/locations/LOCATION/keyRings/KEY_RING

You can retrieve the key ring resource ID using the Cloud Console:

1. Open the Cryptographic Keys page in the Cloud Console.
2. For the key ring whose resource ID you are retrieving, click the More icon (3 vertical dots).
3. Click Copy Resource ID. The resource ID for the key ring is copied to your clipboard.

[key_name] : is the resource ID of the key. This value is case-sensitive and in the form:

projects/PROJECT_ID/locations/LOCATION/keyRings/KEY_RING/cryptoKeys/KEY

You can retrieve the key resource ID using the Cloud Console:

1. Open the Cryptographic Keys page in the Cloud Console.
2. Click the name of the key ring that contains the key.
3. For the key whose resource ID you are retrieving, click the More icon (3 vertical dots).
4. Click Copy Resource ID. The resource ID for the key is copied to your clipboard.

[role] : The role to remove the member from.