Cis Azure Compute 2.3.7

---
name: cis-azure-compute-2.3.7
description: "Ensure 'Minimum Inbound TLS Version' is set to '1.2' or higher"
category: cis-azure-compute
version: "2.0.0"
author: cyberstrike-official
tags: [cis, azure, function-apps, tls, encryption, minimum-tls-version, data-in-transit]
cis_id: "2.3.7"
cis_benchmark: "CIS Microsoft Azure Compute Services Benchmark v2.0.0"
tech_stack: [azure]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 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TLS 1.0 and 1.1 are outdated and vulnerable to security risks.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:

```bash
az functionapp list
```

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

```bash
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:

```powershell
Get-AzFunctionApp
```

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

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

Run the following command to get the TLS version setting:

```powershell
$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:

```bash
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