Cis Azure Compute 2.1.17

Ensure private endpoints used to access App Service apps use private DNS zones

Description

Use private DNS zones to override DNS resolution for a private endpoint. A private DNS zone links a virtual network to an App Service app.

This recommendation assumes application of, and should be applied in conjunction with, the recommendation titled "Ensure private endpoints are used to access App Service apps."

Rationale

It's important to correctly configure DNS settings to ensure that the fully qualified domain name (FQDN) of the App Service app resolves to the private endpoint IP address.

Impact

Incorrectly configured DNS settings may result in unintentional exposure of traffic to the public internet.

Audit Procedure

Using Azure Portal

1. Go to App Services.
2. Click the name of an app.
3. Under Settings, click Networking.
4. Under Inbound traffic configuration, click the link next to Private endpoints.
5. Click the name of a private endpoint.
6. Under Settings, click DNS configuration.
7. Ensure a configuration is displayed with a value for Private DNS zone.
8. Repeat steps 1-7 for each app and private endpoint.

Using Azure CLI

Not specifically documented for this control.

Using Azure PowerShell

Not specifically documented for this control.

Expected Result

Each private endpoint should have a private DNS zone configured.

Remediation

Using Azure Portal

1. Go to App Services.
2. Click the name of an app.
3. Under Settings, click Networking.
4. Under Inbound traffic configuration, click the link next to Private endpoints.
5. Click the name of a private endpoint.
6. Under Settings, click DNS configuration.
7. Click + Add configuration.
8. Select a Subscription, Private DNS zone, and provide a DNS zone group and Configuration name.
9. Click Add.
10. Repeat steps 1-9 for each app and private endpoint requiring remediation.

Using Azure CLI

Not specifically documented for this control.

Using Azure PowerShell

Not specifically documented for this control.

Default Value

Not configured by default.

References

1. https://learn.microsoft.com/en-us/azure/app-service/overview-private-endpoint#dns
2. https://learn.microsoft.com/en-us/azure/private-link/private-endpoint-dns

Profile

Level 2 | Manual