Cis Azure Foundations 9.3.5

Ensure 'Allow Azure services on the trusted services list to access this storage account' is Enabled for Storage Account Access

Description

NOTE: This recommendation assumes that the Public network access parameter is set to Enabled from selected virtual networks and IP addresses. Please ensure the prerequisite recommendation has been implemented before proceeding:

• Ensure Default Network Access Rule for Storage Accounts is Set to Deny

If the Allow Azure services on the trusted services list to access this storage account exception is enabled, the following services are granted access to the storage account: Azure Backup, Azure Data Box, Azure DevTest Labs, Azure Event Grid, Azure Event Hubs, Azure File Sync, Azure HDInsight, Azure Import/Export, Azure Monitor, Azure Networking Services, and Azure Site Recovery (when registered in the subscription).

Rationale

NOTE: If none of the services listed in the Description are in use in your environment, you may wish to make an exception to this recommendation and disable 'Allow Azure services on the trusted services list to access this storage account.'

Turning on firewall rules for a storage account will block access to incoming requests for data, including from other Azure services. Some Azure services that interact with storage accounts operate from networks that can't be granted access through network rules. To help this type of service work as intended, allow the set of trusted Azure services to bypass the network rules. These services will then use strong authentication to access the storage account.

Impact

This creates authentication credentials for services that need access to storage resources so that services will no longer need to communicate via network request. There may be a temporary loss of communication as you set each Storage Account. It is recommended to not do this on mission-critical resources during business hours.

Audit Procedure

Audit from Azure Portal

1. Go to Storage Accounts.
2. For each storage account, under Security + networking, click Networking.
3. Click on the Firewalls and virtual networks heading.
4. Under Exceptions, ensure that Allow Azure services on the trusted services list to access this storage account is checked.

Audit from Azure CLI

Ensure bypass contains AzureServices:

az storage account list --query '[*].networkRuleSet'

Audit from PowerShell

Connect-AzAccount
Set-AzContext -Subscription <subscription ID>
Get-AzStorageAccountNetworkRuleset -ResourceGroupName <resource group> -Name <storage account name> |Select-Object Bypass

If the response from the above command is None, the storage account configuration is out of compliance with this check. If the response is AzureServices, the storage account configuration is in compliance with this check.

Expected Result

bypass should contain AzureServices for all storage accounts.

Remediation

Remediate from Azure Portal

1. Go to Storage Accounts.
2. For each storage account, under Security + networking, click Networking.
3. Click on the Firewalls and virtual networks heading.
4. Under Exceptions, check the box next to Allow Azure services on the trusted services list to access this storage account.
5. Click Save.

Remediate from Azure CLI

Use the below command to update bypass to Azure services.

az storage account update --name <StorageAccountName> --resource-group <resourceGroupName> --bypass AzureServices

Default Value

By default, Storage Accounts will accept connections from clients on any network.

References

1. https://learn.microsoft.com/en-us/azure/storage/common/storage-network-security
2. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-network-security#ns-2-secure-cloud-native-services-with-network-controls

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