Cis Azure Foundations 9.3.2.3

Ensure default network access rule for storage accounts is set to deny

Description

Restricting default network access helps to provide a new layer of security, since storage accounts accept connections from clients on any network. To limit access to selected networks, the default action must be changed.

Rationale

NOTE: This recommendation is only applicable if Public Network Access has not been disabled due to necessity or exception.

Storage accounts should be configured to deny access to traffic from all networks (including internet traffic). Access can be granted to traffic from specific Azure Virtual networks, allowing a secure network boundary for specific applications to be built. Access can also be granted to public internet IP address ranges to enable connections from specific internet or on-premises clients. When network rules are configured, only applications from allowed networks can access a storage account. When calling from an allowed network, applications continue to require proper authorization (a valid access key or SAS token) to access the storage account.

Impact

All allowed networks will need to be whitelisted on each specific network, creating administrative overhead. This may result in loss of network connectivity, so do not turn on for 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 the Firewalls and virtual networks heading.
4. Ensure that Public network access is not set to Enabled from all networks.

Audit from Azure CLI

Ensure defaultAction is not set to Allow.

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 DefaultAction

PowerShell Result - Non-Compliant: DefaultAction : Allow

PowerShell Result - Compliant: DefaultAction : Deny

Expected Result

defaultAction should be set to Deny 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 the Firewalls and virtual networks heading.
4. Set Public network access to Enabled from selected virtual networks and IP addresses.
5. Add rules to allow traffic from specific networks and IP addresses.
6. Click Save.

Remediate from Azure CLI

Use the below command to update default-action to Deny.

az storage account update --name <StorageAccountName> --resource-group <resourceGroupName> --default-action Deny

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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