Configure TLS Fingerprinting

Published April 5, 2023 | Last modified March 11, 2025

Objective

This document provides instructions on how to enhance security for your applications by configuring TLS fingerprinting in your service policy rules. To know more about how F5® Distributed Cloud Services secure your applications using service policies, See Service Policy.

TLS fingerprinting is a method of extracting certain parameters from a TLS client request (ClientHello) and comparing with a predefined or customized set of fingerprints to identify attack patterns. This enhances the protection for your application from DDoS attacks by identifying clients that could be parts of botnets.

TLS fingerprinting from Distributed Cloud Services support the setting of predefined or custom fingerprints using service policy rules. Also, you can obtain the top TLS fingerprints from the virtual host dashboard to update your TLS fingerprint-based service policy rules to dynamically handle the DDoS attacks.

Using the instructions provided in this document, you can create service policies with policy rules to matching the set TLS fingerprints. Per the match conditions, you can set the action of blocking the traffic to secure your applications.

Prerequisites

An F5 Distributed Cloud Account. If you do not have an account, see Getting Started with Console.
An application provisioned using Distributed Cloud Services. Install the Distributed Cloud Services node or cluster image. See Deploy Applications for instructions on how to deploy your applications on Distributed Cloud Services sites.
A virtual host to load balance and serve your application. If you do not have a virtual host, see Virtual Hosts.

Configuration

Configuring the TLS fingerprints and dynamically protecting your application requires the following:

Configuring the service policy with rules that deny the traffic matching configured fingerprints.
Monitoring the virtual host dashboard to check the top TLS fingerprints and update it in the service policy rules to block the associated traffic. This enhances security and reduces the dynamic nature of DDoS attacks by botnets.

Note: You can create a new policy rule or update an existing rule.

Configuration Sequence

Configuring a service policy requires you to perform the following sequence of actions:

Phase	Description
Configure TLS Fingerprints	Create a service policy rule with TLS fingerprints.
Monitor and Update TLS Fingerprints	Obtain the top TLS fingerprints from virtual host dashboard and update the service policy rule with it.

Configure TLS Fingerprints

The TLS fingerprints are applied through the service policies. A service policy requires you to configure service policy rules, apply them to a service policy, and then activate that service policy. This chapter provides instructions on how to set TLS fingerprints in a service policy rule. For detailed instructions on applying a service policy, see Configure a Service Policy.

Step 1: Start service policy creation process.

Log into F5® Distributed Cloud Console (Console).
Click Multi-Cloud App Connect.

Figure: Console Homepage

Select your namespace from the drop-down menu.
Click Security > Service Policies > Service Policies.
Click Add Service Policy.

Step 2: Configure service policy.

In the form, add a name in the Name field.
From the Server Selection menu, select an option.
From the Select Policy Rules menu, select Custom Rule List, and then select Configure.
Click Add Item.
Add a name, and complete the configuration in the Action section. For more information, see Configure a Service Policy guide.

Step 3: Apply predefined TLS fingerprints.

In the Clients section, enable the Show Advanced Fields option.
Under TLS Fingerprint Matcher, click Configure.
From the TLS fingerprint classes menu, select predefined fingerprint classes. These classes include sets of curated fingerprints classified into categories.

Figure: TLS Fingerprint Classes

Optionally, set exact fingerprint values to match:
- In the Exact Values field, click Add Item.
- Click See Common Values and select a value.
- To add more values, click Add Item.
Optionally, set specific fingerprint values to exclude from matching:
- In the Excluded Values field, click Add Item.
- Click See Common Values and select a value.
- To add more values, click Add Item.

Note: Refer to the Classes and Fingerprints guide to find fingerprint classification. This is useful in choosing a fingerprint for excluding in cases where a legitimate fingerprint may belong to one of the predefined classes.

Click Apply to set the TLS fingerprint configuration.
Click Apply to set the new rule.
Click Apply to complete rule configuration.
Click Save and Exit to complete service policy configuration.

Step 4: Activate the service policy.

Click Security > Service Policies > Active Service Policies.
Click Select Active Service Policies.
Find the service policy that was previously created or edited and select it from the menu.
Click Save and Exit.

Step 5: Apply the service policy in the load balancer.

Click Manage > Load Balancers > HTTP Load Balancers.
Find your load balancer and click ... > Manage Configuration > Edit Configuration.
In the Common Security Controls section, perform the following:
- From the Service Policies menu, select Apply Specified Service Policies.
- Click Configure.
- From the menu, select the service policy that was previously created.
- Click Apply.
Click Save and Exit.

Monitor and Update TLS Fingerprint

The load balancer dashboard presents the top TLS fingerprints hitting the domain for your application. You can monitor the dashboard and take the top the TLS fingerprints and apply them in the service policy rule to prevent client requests from matching that fingerprint.

The TLS fingerprints configured in the service policies in the namespace apply to all the load balancers of that namespace.

Step 1: Navigate to load balancer dashboard.

In Console, click Distributed Apps.
Navigate to the namespace of your load balancer.
Click Load Balancers > HTTP Load balancer.

Step 2: Find the top TLS fingerprint from the dashboard.

Find the load balancer for your application from the displayed list and click on it to open the dashboard.
Scroll down to the Top TLS Fingerprints section and note the fingerprint value displayed.

Step 3: Edit the service policy rule to add the fingerprint collected in the previous step.

In the Multi-Cloud App Connect service, navigate to Security > Service Policies > Service Policies.
Click ... > Manage Configuration > Edit Configuration to open the edit form for the service policy created in the Configure TLS Fingerprints chapter.
In the Rules section, click Edit Configuration.
Find the rule and then click ... > Edit.
In the Clients section, enable the Show Advanced Fields section.
In the TLS Fingerprint Matcher field, click Configure.
In the Exact Values field, click Add Item.
Enter the fingerprint you obtained in the previous step.
Click Apply to add the fingerprint value.
Click Apply.
Click Apply to save the new configuration to the service policy rule.
Click Save and Exit to save the service policy configuration.