cis-azure-compute-2-4-14

name	cis-azure-compute-2.4.14
description	Ensure configuration is routed through the virtual network integration
category	cis-azure-compute
version	2.0.0
author	cyberstrike-official
tags	["cis","azure","functions","deployment-slots"]
cis_id	2.4.14
cis_benchmark	CIS Microsoft Azure Compute Services Benchmark v2.0.0
tech_stack	["azure"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure configuration is routed through the virtual network integration

Description

By default, configuration traffic for function app deployment slots goes directly over the public route. Container image pulls and content sharing can be routed through the virtual network integration.

This recommendation applies to function apps using the Premium or Dedicated (App Service) plans, which support deployment slots and virtual networking.

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

Rationale

Route container image pulls and content sharing through a virtual network integration for increased security and control.

Impact

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

Audit Procedure

Using Azure CLI

Run the following command to list function apps:

az functionapp list

For each function app, run the following command to list deployment slots:

az functionapp deployment slot list --resource-group <resource-group-name> --name <function-app-name>

For each deployment slot, ensure that vnetImagePullEnabled and vnetContentShareEnabled are set to true.

Expected Result

Both vnetImagePullEnabled and vnetContentShareEnabled should be set to true.

Remediation

Using Azure CLI

For each deployment slot requiring remediation, run the following command to route container image pulls and content sharing through the virtual network integration:

az resource update --resource-group <resource-group-name> --name <function-app-name>/slots/<deployment-slot-name> --resource-type "Microsoft.Web/sites" --set properties.vnetImagePullEnabled=true --set properties.vnetContentShareEnabled=true

Default Value

By default, configuration traffic goes directly over the public route.

Additional Information

In addition to configuring the routing for content sharing, you must also ensure that any firewall or Network Security Group configured on traffic from the subnet allow traffic to port 443 and 445.

References

1. https://learn.microsoft.com/en-us/azure/app-service/overview-vnet-integration#routes