Setting Up Your Testing Environment

Before you can begin testing web applications, you need to establish a proper testing environment. The most essential tool in any web application security tester's arsenal is an intercepting proxy, and Burp Suite has become the industry standard for good reason.

Why Burp Suite Matters

An intercepting proxy sits between your browser and the websites you're testing, allowing you to capture, analyze, and modify HTTP traffic in real-time. This capability is fundamental to web application testing because it lets you see exactly what's being sent over the wire and manipulate it in ways the application developers never intended.

Burp Suite Community Edition is free and provides enough functionality for most testing scenarios. The Professional edition adds automated scanning, advanced search capabilities, and performance improvements that make it worthwhile for serious professionals.

Initial Configuration

When you first launch Burp Suite, you'll need to configure both the proxy and your browser. By default, Burp listens on localhost port 8080, intercepting any traffic that arrives there. Your browser needs to be configured to send its traffic through this local proxy instead of directly to the internet.

In Firefox, navigate to Settings, search for "proxy," and configure a manual proxy pointing to 127.0.0.1 on port 8080. Make sure to check the box that routes DNS through the proxy as well, otherwise some requests might bypass your interception.

For Chrome users, the FoxyProxy extension provides a convenient way to switch between proxy configurations. You can set up profiles for different testing scenarios and toggle them on and off with a single click.

Handling HTTPS Traffic

Modern websites use HTTPS almost exclusively, which presents a challenge for interception. The entire point of TLS encryption is to prevent man-in-the-middle attacks, and your proxy is essentially performing exactly that kind of attack, albeit on your own traffic.

To make this work, you need to install Burp's Certificate Authority certificate in your browser. Navigate to http://burp while your proxy is running, download the CA certificate, and install it as a trusted root authority. This tells your browser to trust certificates that Burp generates on the fly for each HTTPS site you visit.

Without this step, you'll see constant certificate warnings and be unable to intercept encrypted traffic effectively. However, remember to remove this certificate when you're not actively testing, as leaving it installed creates a security risk.

Your First Interceptions

With everything configured, enable the intercept feature and browse to any website. You should see Burp capture the HTTP request before it reaches the server. Take a moment to explore what you're looking at. The request method, path, and HTTP version appear on the first line. Below that, you'll see various headers including Host, User-Agent, and any cookies that were sent.

Try forwarding the request and watch the response come back. Notice how much information is exchanged even for a simple page load. Each subsequent resource request generates its own HTTP transaction, giving you dozens of opportunities to understand and manipulate the application's behavior.

As you grow more comfortable, you'll learn to let most traffic pass through uninspected while focusing your attention on the requests that matter most, typically those involving authentication, data submission, and API calls. Setting an appropriate scope helps Burp filter traffic so you only see what's relevant to your current testing target.