Cis Azure Compute 2.4.4

Ensure 'FTP state' is set to 'FTPS only' or 'Disabled'

Description

By default, App Service supports deployment over FTP. If FTP is essential for a deployment workflow, FTPS should be enforced for all function app deployment slots.

If FTPS is not explicitly required, the recommended setting is Disabled.

Rationale

FTP is an unencrypted network protocol that transmits data -- including passwords -- in clear text. The use of this protocol can lead to both data and credential compromise and can present opportunities for exfiltration, persistence, and lateral movement.

Impact

Deployment workflows that rely on FTP or FTPS rather than WebDeploy or HTTPS endpoints may be affected.

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 pane, under Platform settings, ensure that FTP state is set to FTPS only or Disabled.
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 FTPS state setting:

az resource show --name web --resource-group <resource-group-name> --namespace Microsoft.Web --resource-type config --parent sites/<function-app-name>/slots/<deployment-slot-name> --query properties.ftpsState

Ensure that "FtpsOnly" or "Disabled" is returned.

Expected Result

The ftpsState property should return "FtpsOnly" or "Disabled".

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 FTP state to FTPS only or Disabled.
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 set FTPS state to FtpsOnly or Disabled:

az resource update --name web --resource-group <resource-group-name> --namespace Microsoft.Web --resource-type config --parent sites/<function-app-name>/slots/<deployment-slot-name> --set properties.ftpsState=<FtpsOnly|Disabled>

Default Value

By default, FTP state is set to FTPS only.

References

1. https://learn.microsoft.com/en-us/azure/app-service/deploy-ftp
2. https://learn.microsoft.com/en-us/azure/app-service/overview-security
3. https://learn.microsoft.com/en-us/azure/azure-functions/functions-how-to-use-azure-function-app-settings#ftps-deployment-settings
4. https://learn.microsoft.com/en-us/cli/azure/functionapp
5. https://learn.microsoft.com/en-us/cli/azure/resource
6. https://learn.microsoft.com/en-us/security/benchmark/azure/security-controls-v3-data-protection#dp-4-encrypt-sensitive-information-in-transit
7. https://learn.microsoft.com/en-us/security/benchmark/azure/security-controls-v3-posture-vulnerability-management#pv-7-rapidly-and-automatically-remediate-software-vulnerabilities

Profile

Level 1 | Automated