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

Overview

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

Rationale

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. Only applications from allowed networks can access a storage account when network rules are configured. 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 a loss of network connectivity, so do not turn on critical resources during business hours.

Default Value

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

References

Remediation guidance

Azure Console

Open the storage account in the Azure Portal using the Open in Azure button.
Under Networking, click the Firewalls and virtual networks heading.
Ensure that, under Public network access, Enabled from all networks is not selected
Click Save to apply your changes

Azure CLI

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

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

Multiple Remediation Paths

Azure

SERVICE-WIDE (RECOMMENDED when many resources are affected): Assign Azure Policy initiatives at management group/subscription scope and trigger remediation tasks.

az policy assignment create --name <assignment-name> --scope /subscriptions/<subscription-id> --policy-set-definition <initiative-id>
az policy remediation create --name <remediation-name> --policy-assignment <assignment-id>

ASSET-LEVEL: Apply the resource-specific remediation steps above to the listed non-compliant resources.

PREVENTIVE: Embed Azure Policy checks into landing zones and IaC workflows to block or auto-remediate drift.

References for Service-Wide Patterns

Azure Policy overview: https://learn.microsoft.com/en-us/azure/governance/policy/overview
Azure Policy remediation: https://learn.microsoft.com/en-us/azure/governance/policy/how-to/remediate-resources
Azure Policy initiative structure: https://learn.microsoft.com/en-us/azure/governance/policy/concepts/initiative-definition-structure

Operational Rollout Workflow

Use this sequence to reduce risk and avoid repeated drift.

1. Contain at Service-Wide Scope First (Recommended)

Azure: assign policy initiatives at management group/subscription scope and run remediation tasks.

az policy assignment create --name <assignment-name> --scope /subscriptions/<subscription-id> --policy-set-definition <initiative-id>
az policy remediation create --name <remediation-name> --policy-assignment <assignment-id>

2. Remediate Existing Affected Assets

Execute the control-specific Console/CLI steps documented above for each flagged resource.
Prioritize internet-exposed and production assets first.

3. Validate and Prevent Recurrence

Re-scan after each remediation batch.
Track exceptions with owner and expiry date.
Add preventive checks in IaC/CI pipelines.

Query logic

These are the stored checks tied to this control.

Storage accounts with the default action not set to Deny

Connectors

Microsoft Azure

Covered asset types

StorageAccount

Expected check: eq []

{
  storageAccounts(where: { NOT: { networkRuleSetDefaultAction: "Deny" } }) {
    ...AssetFragment
  }
}