Cloud KMS cryptokeys should restrict anonymous and/or public access

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Description

It is recommended that the IAM policy on Cloud KMS cryptokeys should restrict anonymous and/or public access.

Rationale

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.

Default Value

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

Impact

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

Additional Information

key_ring_name is the resource ID of the key ring, which is the fully-qualified key ring name. This value is case-sensitive and in the format: 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 kebab menu (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, which is the fully-qualified CryptoKey name. This value is case-sensitive and in the format: 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 ring whose resource ID you are retrieving, click the kebab menu (3 vertical dots).
  4. Click Copy Resource ID. The resource ID for the key ring is copied to your clipboard.

role is the role to remove the member from.

Finding Notes

Findings may be inconsistent while gcloud kms keyrings get-iam-policy is implemented.

Manual audits may be performed using

  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[]'

Remediation

From the command line

  1. List all Cloud KMS Cryptokeys.
    gcloud kms keys list --keyring=[key_ring_name] --location=global --format=json | jq '.[].name'
  2. To remove access to allUsers and allAuthenticatedUsers, remove the IAM policy binding for a KMS key using the below command.
gcloud kms keys remove-iam-policy-binding [key_name] --keyring=[key_ring_name] --location=global --member='allAuthenticatedUsers' --role='[role]'

gcloud kms keys remove-iam-policy-binding [key_name] --keyring=[key_ring_name] --location=global --member='allUsers' --role='[role]'

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