Cis Azure Compute 2.3.7

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 apps 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TLS 1.0 and 1.1 are outdated and vulnerable to security risks.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 Settings, click Configuration.
4. In the General settings pane, under Platform settings, ensure that Minimum Inbound TLS Version is set to 1.2 or higher.
5. Repeat steps 1-4 for each function app.

Using Azure CLI

Run the following command to list function apps:

az functionapp list

For each function app, run the following command to get the TLS version setting:

az functionapp config show --resource-group <resource-group-name> --name <function-app-name> --query minTlsVersion

Ensure that "1.2" or higher is returned.

Using Azure PowerShell

Run the following command to list function apps:

Get-AzFunctionApp

Run the following command to get the function app in a resource group with a given name:

$app = Get-AzFunctionApp -ResourceGroupName <resource-group-name> -Name <function-app-name>

Run the following command to get the TLS version setting:

$app.SiteConfig.MinTlsVersion

Ensure that the command returns 1.2 or higher. Repeat for each function app.

Expected Result

The minimum TLS version should be 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 Settings, click Configuration.
4. In the General settings pane, under Platform settings, click the drop-down next to Minimum Inbound TLS Version and select 1.2 or higher.
5. Click Save.
6. Click Continue.
7. Repeat steps 1-6 for each function app requiring remediation.

Using Azure CLI

For each function app requiring remediation, run the following command to update the TLS version:

az functionapp config set --resource-group <resource-group-name> --name <function-app-name> --min-tls-version <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/powershell/module/az.functions/get-azfunctionapp
6. https://csrc.nist.gov/news/2019/nist-publishes-sp-800-52-revision-2

Profile

Level 1 | Automated