Cis Azure Compute 2.4.7

Ensure 'Minimum Inbound TLS Version' is set to '1.2' or higher

Description

The TLS (Transport Layer Security) protocol secures the transmission of data over the internet using standard encryption technology. Function app deployment slots use TLS 1.2 for the Minimum Inbound TLS Version by default and allow for the use of TLS versions 1.0, 1.1, and 1.3. NIST strongly suggests the use of TLS 1.2 and recommends the adoption of TLS 1.3.

Rationale

TLS 1.0 and 1.1 are outdated and vulnerable to security risks. Since TLS 1.2 and TLS 1.3 provide enhanced security and improved performance, it is highly recommended to use TLS 1.2 or higher whenever possible.

Impact

Using the latest TLS version may affect compatibility with clients and backend services.

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 Minimum Inbound TLS Version is set to 1.2 or higher.
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 <app-name>

For each deployment slot, run the following command to get the TLS version 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.minTlsVersion

Ensure that "1.2" or higher is returned.

Expected Result

The minTlsVersion property should return "1.2" or higher.

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, click the drop-down next to Minimum Inbound TLS Version and select 1.2 or higher.
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 update the TLS version:

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.minTlsVersion=<1.2|1.3>

Default Value

By default, TLS version is set to 1.2.

References

1. https://learn.microsoft.com/en-us/azure/app-service/configure-ssl-bindings#how-can-i-change-the-minimum-tls-versions-for-the-app
2. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-data-protection#dp-3-encrypt-sensitive-data-in-transit
3. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-network-security#ns-8-detect-and-disable-insecure-services-and-protocols
4. https://learn.microsoft.com/en-us/cli/azure/functionapp
5. https://learn.microsoft.com/en-us/cli/azure/resource
6. https://csrc.nist.gov/news/2019/nist-publishes-sp-800-52-revision-2

Profile

Level 1 | Automated