When clients make requests to your application, Barracuda WAF-as-a-Service detects violations and takes actions that correspond to the severity of the violation. For details on the various actions, refer to Violation Responses - Policy Options. 

You can leave the default actions as is, or customize them to suit the specific needs of your organization.

Understanding Risk Scores  

There are two types of risk scores that can be computed and then used to detect malicious requests or clients.

• Request Risk Score

• Client Risk Score

Request Risk Score

Every incoming request is evaluated by the Barracuda WAF-as-a-Service on multiple parameters. As multiple aspects of requests are evaluated, each deviation from the expected structure and behavior contributes to the risk score for that specific request.

Each deviation detected by the Barracuda WAF-as-a-Service is associated with an attack ID. The risk metric associated with each attack ID provides the weights used to compute the Request Risk Score.

A request identified with one deviation shows the same risk score, whereas a request identified with two or more deviations shows the weighted sum of all the risk scores in the Access log. In Web Firewall logs, for service in “Passive” mode, multiple logs are generated for the same request (i.e., the same ID), so the risk scores are shown in individual logs, adding themselves with every identified attack.

Client Risk Score

Metadata from each request and response is sent to the cloud-based Barracuda Application Intelligence Network. This information is analyzed for each session, and the risk of the client is computed based on the traffic and the client’s behavioral characteristics.

This score is used to identify the risk of a specific client - whether the client is good, suspicious, or bad.

Some of the characteristics used to compute the score for a client are:

• Attacks on the applications in the given session

• Statistical anomalies in the client session

• Suspicious client fingerprints, devices, etc.  Fingerprints include information about the browser attributes from all the devices that the client uses during login.

• Previous anomalous behavior exhibited by the client

Risk Levels 

These risk scores are used as standards and cannot be modified:

• 100 - Critical

• 80 - High

• 60 - Elevated

• 40 - Medium

• 20 - Low

Understanding Client Fingerprinting

In the process of client fingerprinting, Barracuda WAF-as-a-Service collects information about the browser attributes from all the devices that the client uses during login. This collected information helps Barracuda WAF-as-a-service identify suspicious clients (potential bots) and recognize web scraping attacks more quickly.  Clients are often identified solely by their IP address. But depending on IP addresses is not always accurate, based on these examples:

• Blocking a client IP address that is behind a NATed network can also block other, valid users.

• The same client can jump IP addresses or use proxies to hide their actual location.

With client fingerprinting, Barracuda WAF-as-a-Service can identify a specific client down to the browser, so other, valid clients are not affected. 

Data used to identify clients using fingerprinting include:

• characteristics of the client’s system

• request analysis based on incoming traffic

• SSL information

Understanding Tarpits

As the name implies, within a tarpit, everything moves very slowly. When a client repeatedly attempts to access your application, Barracuda WAF-as-a-Service can intentionally delay those incoming requests with a tarpit. This slow processing often makes bad clients give up, rather than keep trying, protecting your application. On the Policy Options page, you can specify a limit for the number of requests that a single client can make. After that number is reached, the client is put into a tarpit. Their requests are put in a backlog and are only processed after active requests are served and then only after the time delay interval between requests that you specify. The client remains in the tarpit for the amount of time you specify and is then released. 

Editing Response Policies

To edit a response policy:

1. On the Barracuda WAF-as-a-Service dashboard, click the link for the desired application.

2. In the left navigation, select Violation Responses, then Response Policies. If it is not present, click Add Components and add it. 

3. Locate the violation that you want to edit. Note that there are over 200 violations, so you might want to use the Search function or view all pages of violations. 

4. In the More column, click the three dots and select Edit Response. 

5. Edit some or all of the values, then click Save. 
   Specify a new Risk Level.