Control: 9.4 Ensure the web app has 'Client Certificates (Incoming client certificates)' set to 'On'

Description

Client certificates allow for the app to request a certificate for incoming requests. Only clients that have a valid certificate will be able to reach the app. The TLS mutual authentication technique in enterprise environments ensures the authenticity of clients to the server. If incoming client certificates are enabled, then only an authenticated client who has valid certificates can access the app.

As default, incoming client certificates is set to Ignore.

Remediation

From Console

Login to Azure Portal and go to App Services.
Click on each App.
Under Settings section, click on Configuration.
Go to General settings tab.
Set the option Client certificate mode located under Incoming client certificates is set to Require.

From Command Line

To set Incoming client certificates value for an existing app:

az webapp update --resource-group <RESOURCE_GROUP_NAME> --name <APP_NAME> -- set clientCertEnabled=true

Usage

Run the control in your terminal:

powerpipe control run azure_compliance.control.cis_v140_9_4

Snapshot and share results via Turbot Pipes:

powerpipe login
powerpipe control run azure_compliance.control.cis_v140_9_4 --share

SQL

This control uses a named query:

select
  app.id as resource,
  case
    when not client_cert_enabled then 'alarm'
    else 'ok'
  end as status,
  case
    when not client_cert_enabled then name || ' incoming client certificates set to off.'
    else name || ' incoming client certificates set to on.'
  end as reason
  
  , app.resource_group as resource_group
  , sub.display_name as subscription
from
  azure_app_service_web_app as app,
  azure_subscription as sub
where
  sub.subscription_id = app.subscription_id;