Cis Azure Compute 2.4.6

Ensure 'HTTPS Only' is set to 'On'

Description

Azure App Service allows function app deployment slots to run under both HTTP and HTTPS by default. Function app deployment slots can be accessed by anyone using non-secure HTTP links by default. Non-secure HTTP requests can be restricted and all HTTP requests redirected to the secure HTTPS port. It is recommended to enforce HTTPS-only traffic.

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

Rationale

Enabling HTTPS-only traffic will redirect all non-secure HTTP requests to HTTPS ports. HTTPS uses the TLS/SSL protocol to provide a secure connection which is both encrypted and authenticated. It is therefore important to support HTTPS for the security benefits.

Impact

When it is enabled, every incoming HTTP request is redirected to the HTTPS port. This means an extra level of security will be added to the HTTP requests made to the deployment slot.

Audit Procedure

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 tab, under Platform settings, ensure that HTTPS Only is set to On.
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, ensure that httpsOnly is set to true.

Expected Result

The httpsOnly property should be set to true.

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 tab, under Platform settings, next to HTTPS Only, select the radio button next to On.
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 enable HTTPS Only:

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

Default Value

HTTPS Only is enabled by default.

References

1. https://learn.microsoft.com/en-us/azure/app-service/overview-security#https-and-certificates
2. https://learn.microsoft.com/en-us/security/benchmark/azure/security-controls-v3-data-protection#dp-3-encrypt-sensitive-data-in-transit
3. https://techcommunity.microsoft.com/t5/azure-paas-blog/enable-https-setting-on-azure-app-service-using-azure-policy/ba-p/3286603
4. https://learn.microsoft.com/en-us/azure/azure-functions/security-concepts
5. https://learn.microsoft.com/en-us/azure/azure-functions/functions-deployment-slots
6. https://learn.microsoft.com/en-us/cli/azure/functionapp
7. https://learn.microsoft.com/en-us/cli/azure/resource

Profile

Level 1 | Automated