Cis Azure Compute 15.1

Ensure Batch account is set to use customer-managed keys to encrypt data

Description

Customer-managed keys introduce additional depth to security by providing a means to manage access control for encryption keys. Where compliance and security frameworks indicate the need, and organizational capacity allows, sensitive data at rest can be encrypted using customer-managed keys (CMK) rather than Microsoft-managed keys.

While it is possible to automate the assessment of this recommendation, the assessment status for this recommendation remains 'Manual' due to ideally limited scope. The scope of application -- which workloads CMK is applied to -- should be carefully considered to account for organizational capacity and targeted to workloads with specific need for CMK.

Rationale

By default in Azure, data at rest tends to be encrypted using Microsoft-managed keys. If your organization wants to control and manage encryption keys for compliance and defense-in-depth, customer-managed keys can be established.

Impact

If the key expires due to setting the 'activation date' and 'expiration date', the key must be rotated manually.

Using customer-managed keys may also incur additional man-hour requirements to create, store, manage, and protect the keys as needed.

Audit Procedure

Using Azure Portal

1. Login to Azure Portal using https://portal.azure.com
2. Navigate to Batch accounts

For each Batch account perform the following:

1. Under the Settings section, click on Encryption
2. Ensure that the Customer-managed key radio button is selected
3. Ensure that a key vault key is set and valid

If no key vault key is set, the configuration fails this audit procedure.

Using Azure CLI

The following command should return the Key URL and source Key Vault:

az batch account show --name <batch-account-name> --resource-group <resource-group-name> --query "keyVaultReference"

If the result is null or Empty, the configuration fails this audit procedure.

Using Azure PowerShell

Set-AzBatchAccount -ResourceGroupName <resource_group_name> -AccountName <batch_account_name> `
  -KeyVaultReferenceId "/subscriptions/<subscription_ID>/resourceGroups/<resource_group_name>/providers/Microsoft.KeyVault/vaults/<keyvault_name>" `
  -KeyVaultReferenceUrl "https://<keyvault_name>.vault.azure.net/keys/<key_name>"

Expected Result

The Batch account should have Customer-managed key encryption selected with a valid key vault key configured. The keyVaultReference should not be null or empty.

Remediation

Using Azure Portal

1. Login to Azure Portal using https://portal.azure.com
2. Navigate to Batch accounts

For each Batch account:

1. Under the Settings section, click on Encryption
2. Select the Customer-managed key radio button
3. Use either Enter key URI or Select from key vault to select and set the encryption key.

Using Azure CLI

# Link CMK to Batch account
az batch account set \
  --resource-group <resource_group_name> \
  --name <batch_account_name> \
  --encryption-key-identifier https://<keyvault_name>.vault.azure.net/keys/<key_name>/<Version>

Using Azure PowerShell

Set-AzBatchAccount -ResourceGroupName <resource_group_name> -AccountName <batch_account_name> `
  -KeyVaultReferenceId "/subscriptions/<subscription_ID>/resourceGroups/<resource_group_name>/providers/Microsoft.KeyVault/vaults/<keyvault_name>" `
  -KeyVaultReferenceUrl "https://<keyvault_name>.vault.azure.net/keys/<key_name>"

Default Value

Azure Batch accounts uses Microsoft-managed keys (service-managed encryption) for data at rest by default.

References

1. https://learn.microsoft.com/en-us/azure/batch/batch-customer-managed-key

Profile

Level 2 | Manual