Cis Azure Compute 2.3.16

Ensure all traffic is routed through the virtual network

Description

Enable vnetRouteAllEnabled to ensure all outbound traffic is routed through the integrated virtual network.

This recommendation should be applied after integrating a function app with a virtual network.

Rationale

Routing all outbound traffic through the virtual network enhances security.

Impact

Additional configuration may be required to ensure that traffic is routed properly.

Audit Procedure

Using Azure Portal

1. Go to App Services or Function App.
2. Click the name of a function app.
3. Under Settings, click Networking.
4. Under Outbound traffic configuration, next to Virtual network integration, click the virtual network and subnet name.
5. Under Application routing, ensure that the box next to Outbound internet traffic is checked.
6. Repeat steps 1-5 for each function app.

Using Azure CLI

Run the following command to list function apps:

az functionapp list

For each function app, run the following command to get the virtual network traffic routing setting:

az functionapp show --resource-group <resource-group-name> --name <app-name> --query vnetRouteAllEnabled

Ensure that true is returned.

Expected Result

The vnetRouteAllEnabled setting should return true.

Remediation

Using Azure Portal

1. Go to App Services or Function App.
2. Click the name of a function app.
3. Under Settings, click Networking.
4. Under Outbound traffic configuration, next to Virtual network integration, click the virtual network and subnet name.
5. Under Application routing, check the box next to Outbound internet traffic.
6. Click Apply.
7. Repeat steps 1-6 for each function app requiring remediation.

Using Azure CLI

For each function app requiring remediation, run the following command to route all traffic through the virtual network:

az resource update --resource-group <resource-group-name> --name <function-app-name> --resource-type "Microsoft.Web/sites" --set properties.vnetRouteAllEnabled=true

Default Value

For function apps integrated with a virtual network, all traffic is routed through the virtual network by default.

References

1. https://learn.microsoft.com/en-us/azure/app-service/configure-vnet-integration-routing#configure-application-routing
2. https://learn.microsoft.com/en-us/azure/azure-functions/functions-app-settings#vnetrouteallenabled
3. https://learn.microsoft.com/en-us/cli/azure/functionapp
4. https://learn.microsoft.com/en-us/cli/azure/resource

Profile

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