GCP KMS crypto key is anonymously accessible

Description

It is recommended that the IAM policy on Cloud KMS cryptokeys should restrict anonymous and/or public access.
Granting permissions to allUsers or allAuthenticatedUsers allows anyone to access the dataset. Such access might not be desirable if sensitive data is stored at the location. In this case, ensure that anonymous and/or public access to a Cloud KMS cryptokey is not allowed.

Fix - Buildtime

Terraform

Resource: google_kms_crypto_key
Argument: google_kms_crypto_key_iam_member / google_kms_crypto_key_iam_binding

resource "google_kms_key_ring" "keyring" {
  name = "keyring-example"
  location = "global"
}

resource "google_kms_crypto_key" "bad_key" {
  name = "crypto-key-example"
  key_ring = google_kms_key_ring.keyring.id
  rotation_period = "100000s"
  lifecycle {
    prevent_destroy = true
  }
}

resource "google_kms_crypto_key_iam_member" "bad_member_1" {
  crypto_key_id = google_kms_crypto_key.bad_key.id
  role          = "roles/cloudkms.cryptoKeyEncrypter"
- member        = "allUsers"
}

resource "google_kms_crypto_key_iam_member" "bad_member_2" {
  crypto_key_id = google_kms_crypto_key.bad_key.id
  role          = "roles/cloudkms.cryptoKeyEncrypter"
- member        = "allAuthenticatedUsers"
}

resource "google_kms_crypto_key_iam_binding" "bad_binding_1" {
  crypto_key_id = google_kms_crypto_key.bad_key.id
  role          = "roles/cloudkms.cryptoKeyEncrypter"
- members = [
-   "allUsers",
- ]
}

resource "google_kms_crypto_key_iam_binding" "bad_binding_2" {
  crypto_key_id = google_kms_crypto_key.bad_key.id
  role          = "roles/cloudkms.cryptoKeyEncrypter"
- members = [
-   "allAuthenticatedUsers",
- ]
}

resource "google_kms_crypto_key" "good_key" {
  name = "crypto-key-example"
  key_ring = google_kms_key_ring.keyring.id
  rotation_period = "100000s"
  lifecycle {
    prevent_destroy = true
  }
}

resource "google_kms_crypto_key_iam_member" "good_member" {
  crypto_key_id = google_kms_crypto_key.good_key.id
  role = "roles/cloudkms.cryptoKeyEncrypter"
+ member = "user:[email protected]"
}

resource "google_kms_crypto_key_iam_binding" "good_binding" {
  crypto_key_id = google_kms_crypto_key.good_key.id
  role          = "roles/cloudkms.cryptoKeyEncrypter"
+ members = [
+   "user:[email protected]",
+ ]
}