Cis Azure Compute 2.3.14

Ensure function app is integrated with a virtual network

Description

Integrate function apps with a virtual network to enable access to resources in or through a non-internet-routable virtual network.

This recommendation does not apply to function apps created on the consumption hosting plan, which does not support virtual networking.

Rationale

Integrate function apps with a virtual network for increased security and control.

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, ensure that a virtual network and subnet name are displayed.
5. Repeat steps 1-4 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 subnet ID:

az functionapp show --resource-group <resource-group-name> --name <function-app-name> --query "virtualNetworkSubnetId"

Ensure that a virtual network subnet ID is returned.

Using Azure PowerShell

Run the following command to list function apps:

Get-AzFunctionApp

Run the following command to get the function app in a resource group with a given name:

$app = Get-AzFunctionApp -ResourceGroupName <resource-group-name> -Name <function-app-name>

Run the following command to get the virtual network subnet ID:

$app.virtualNetworkSubnetId

Ensure that a virtual network subnet ID is returned. Repeat for each function app.

Expected Result

A virtual network subnet ID should be returned (not null or empty).

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 Not configured.
5. Click Add virtual network integration.
6. Select an existing App Service Plan connection, or select New connection and select a subscription, virtual network, and subnet.
7. Click Connect.
8. Repeat steps 1-7 for each function app requiring remediation.

Using Azure CLI

For each function app requiring remediation, run the following command to integrate with a virtual network:

az functionapp vnet-integration add --resource-group <resource-group-name> --name <function-app-name> --vnet <virtual-network-name> --subnet <subnet-name>

Using Azure PowerShell

For each function app requiring remediation, run the following commands to integrate with a virtual network:

Prepare parameters:

$siteName = '<app-name>'
$vNetResourceGroupName = '<virtual-network-resource-group-name>'
$functionAppResourceGroupName = '<function-app-resource-group-name>'
$vNetName = '<virtual-network-name>'
$integrationSubnetName = '<subnet-name>'
$vNetSubscriptionId = '<subscription-guid>'

Check if the subnet is delegated to Microsoft.Web/serverFarms:

$vnet = Get-AzVirtualNetwork -Name $vNetName -ResourceGroupName $vNetResourceGroupName
$subnet = Get-AzVirtualNetworkSubnetConfig -Name $integrationSubnetName -VirtualNetwork $vnet
Get-AzDelegation -Subnet $subnet

Add delegation:

$subnet = Add-AzDelegation -Name "myDelegation" -ServiceName "Microsoft.Web/serverFarms" -Subnet $subnet
Set-AzVirtualNetwork -VirtualNetwork $vnet

Configure virtual network integration:

$subnetResourceId = "/subscriptions/$vNetSubscriptionId/resourceGroups/$vNetResourceGroupName/providers/Microsoft.Network/virtualNetworks/$vNetName/subnets/$integrationSubnetName"
$functionApp = Get-AzResource -ResourceType Microsoft.Web/sites -ResourceGroupName $functionAppResourceGroupName -ResourceName $siteName
$functionApp.Properties.virtualNetworkSubnetId = $subnetResourceId
$functionApp.Properties.vnetRouteAllEnabled = 'true'
$functionApp | Set-AzResource -Force

Default Value

By default, virtual network integration is not configured.

References

1. https://learn.microsoft.com/en-us/azure/azure-functions/functions-networking-options
2. https://learn.microsoft.com/en-us/azure/app-service/overview-vnet-integration
3. https://learn.microsoft.com/en-us/azure/app-service/configure-vnet-integration-enable
4. https://learn.microsoft.com/en-us/cli/azure/functionapp
5. https://learn.microsoft.com/en-us/powershell/module/az.functions/get-azfunctionapp

Profile

Level 1 | Automated