Ensure 'Firewalls & Networks' Is Limited to Use Selected Networks Instead of All Networks for Cosmos DB

Overview

Limiting your Cosmos DB to only communicate on whitelisted networks lowers its attack footprint.

Rationale

Selecting certain networks for your Cosmos DB to communicate restricts the number of networks, including the internet, that can interact with what is stored within the database.

Impact

WARNING: Failure to whitelist the correct networks will result in a connection loss.

WARNING: Changes to Cosmos DB firewalls may take up to 15 minutes to apply. To avoid disruption, ensure that sufficient time is planned for remediation or changes.

Default Value

By default, Cosmos DBs allow access from all networks.

Remediation guidance

Remediate from Azure Portal

Open the Cosmos DB account using the Open in Azure button
Select Networking.
Under Public network access, select Selected networks.
Under Virtual networks, select + Add existing virtual network or + Add a new virtual network.
For existing networks, select subscription, virtual network, subnet and click Add. For new networks, provide a name, update the default values if required, and click Create.
Click Save.

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.

Azure Cosmos DB Accounts Allowing All Networks

Connectors

Microsoft Azure

Covered asset types

CosmosDBAccount

Expected check: eq []

{
  cosmosDbAccounts(where: { isVirtualNetworkFilterEnabled: false }) {
    ...AssetFragment
  }
}