Cis Azure Compute 2.4.3

Ensure 'Basic Authentication Publishing Credentials' are 'Disabled'

Description

Basic Authentication Publishing Credentials provides the ability to publish -- or deploy to -- a function app deployment slot without a centralized Identity Provider. For a more effective, capable, and secure solution for Identity, Authentication, Authorization, and Accountability, a centralized Identity Provider such as Entra ID is strongly advised.

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

Rationale

Basic Authentication introduces an identity silo for privileged access to a resource and produces logging which may not provide a full chain of accountability. This can be exploited in numerous ways and represents a significant vulnerability and attack vector.

Impact

Disabling 'Basic Auth Publishing Credentials' will prevent the following deployment methods from working:

FTP Basic Auth Publishing Credentials:

• FTP
• FTPS

SCM Basic Auth Publishing Credentials:

• Local Git
• GitHub
• Azure Repos
• Bitbucket
• Visual Studio (Version 17.12 and earlier)

If this recommendation cannot be implemented because one of the above listed deployment methods is necessary and cannot be adapted, compensating controls (e.g. using FTPS Only and disabling only "SCM Basic Auth Publishing Credentials") are recommended to reduce potential attack surface.

An Identity Provider that can be used by the function app deployment slot for authenticating users is required.

Audit Procedure

Using Azure Portal

1. Go to App Services or Function App.
2. Click the name of an app.
3. Under Deployment, click Deployment slots.
4. Click the name of a deployment slot.
5. Under Settings, click Configuration.
6. In the General settings pane, under Platform settings, ensure that SCM Basic Auth Publishing Credentials and FTP Basic Auth Publishing Credentials are set to Off.
7. Repeat steps 1-6 for each function app and deployment slot.

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, run the following command to get the basic authentication for FTP setting:

az resource show --resource-group <resource-group-name> --name ftp --namespace Microsoft.Web --resource-type basicPublishingCredentialsPolicies --parent sites/<function-app-name>/slots/<deployment-slot-name> --query properties.allow

Ensure that false is returned.

For each deployment slot, run the following command to get the basic authentication for SCM setting:

az resource show --resource-group <resource-group-name> --name scm --namespace Microsoft.Web --resource-type basicPublishingCredentialsPolicies --parent sites/<function-app-name>/slots/<deployment-slot-name> --query properties.allow

Ensure that false is returned.

Expected Result

Both FTP and SCM basic authentication publishing credentials should return false for properties.allow.

Remediation

Using Azure Portal

1. Go to App Services or Function App.
2. Click the name of a function app.
3. Under Deployment, click Deployment slots.
4. Click the name of a deployment slot.
5. Under Settings, click Configuration.
6. In the General settings pane, under Platform settings, set SCM Basic Auth Publishing Credentials and FTP Basic Auth Publishing Credentials to Off.
7. Click Save.
8. Click Continue.
9. Repeat steps 1-8 for each function app and deployment slot requiring remediation.

Using Azure CLI

For each deployment slot requiring remediation, run the following command to disable basic authentication for FTP:

az resource update --resource-group <resource-group-name> --name ftp --namespace Microsoft.Web --resource-type basicPublishingCredentialsPolicies --parent sites/<function-app-name>/slots/<deployment-slot-name> --set properties.allow=false

For each deployment slot requiring remediation, run the following command to disable basic authentication for SCM:

az resource update --resource-group <resource-group-name> --name scm --namespace Microsoft.Web --resource-type basicPublishingCredentialsPolicies --parent sites/<function-app-name>/slots/<deployment-slot-name> --set properties.allow=false

Default Value

Basic authentication is enabled by default.

References

1. https://learn.microsoft.com/en-us/azure/app-service/configure-basic-auth-disable
2. https://learn.microsoft.com/en-us/cli/azure/functionapp
3. https://learn.microsoft.com/en-us/cli/azure/resource

Profile

Level 1 | Automated