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Introduction to Web Applications
OSCP · Chapter 5

Introduction to Web Applications

Modern penetration testing spends most of its time on web applications, since they are the most common attacker-facing surface. Understanding HTTP requests, sessions, and how the client/server boundary is trusted (or not) is the prerequisite for everything else in this track.

Key concepts

  • Every request/response pair is an opportunity: headers, cookies, hidden form fields and query parameters are all attacker-controllable input.
  • A proxy (Burp Suite / OWASP ZAP) sitting between browser and server is the single most useful tool for web testing — it lets you intercept, replay and fuzz requests.
  • Understand trust boundaries: anything sent from the browser must be treated as untrusted by the server, no matter how much client-side validation exists.
  • Map the application first (spidering, auth flows, API endpoints) before attacking anything — you cannot test what you have not found.

Try it yourself

Install Burp Suite Community Edition, configure your browser to proxy through it, and browse any lab application. Inspect one request/response pair and identify every piece of client-controlled data in it.

@ Daniel Burlacu