Lesson 1 of 15

OWASP Top 10 Overview

The OWASP Top 10 is the definitive reference for the most critical web application security risks, updated regularly based on real-world vulnerability data. You will learn what each category means, why it appears on the list, and how developers and testers approach it. This overview provides the framework for everything covered in the rest of this course.

Learning Objectives — Deep Dive

Each objective below is broken down into plain English so you know exactly what you are learning, why it matters, and what you will be able to do when you are done. Mark each one complete as you work through the lesson.

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In plain English

This is asking you to build a clear mental model of the concept — not just memorize a definition, but genuinely understand what it means, why it exists, and how it connects to everything else you are learning. When you can explain "the OWASP Top 10 2021 categories" in your own words to someone who has never heard of it, you have truly learned it.

Why this matters

Web applications are the most common attack surface in modern security. The OWASP Top 10 vulnerabilities alone account for the majority of real-world breaches. Mastering web application security opens the door to bug bounty programs, penetration testing contracts, and application security roles.

Real-world analogy

Think of it like learning to drive. You do not need to understand how the engine works to drive safely, but knowing the basics helps you diagnose problems and avoid mistakes that could cause accidents. The same principle applies here — foundational knowledge prevents costly errors.

What you will be able to do

Apply this skill in a real lab environment, explain it clearly to a colleague or client, and use it as a building block for the more advanced techniques that come later in this course.

Beginner tip

Do not try to memorize everything at once. Read through the material once to get the big picture, then go back and work through the lab. The hands-on practice is what makes the concepts stick — passive reading alone will not get you there.

OWASP Top 10 Overview · Objective 1 of 4

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Visit the OWASP Top 10 website

Navigate to owasp.org/www-project-top-ten/ to access the official OWASP Top 10 list, which is updated every few years to reflect the most critical web application security risks. Bookmark the page and note the year of the current edition — the 2021 list differs significantly from the 2017 list, so always reference the most recent version. The OWASP Top 10 is the industry-standard baseline for web application security assessments and is referenced in virtually every penetration testing methodology. Understanding why each category made the list is as important as knowing what it is.

Read each category description

Work through each of the 10 categories in order, reading the full description, example attack scenarios, and prevention guidance for each one. Pay particular attention to the 'How to Prevent' section — understanding defenses helps you recognize when they are absent during a real assessment. Take notes on the categories that are new to you, especially Insecure Design (A04) and Software and Data Integrity Failures (A08) which were added in 2021. Allocate at least 10–15 minutes per category to absorb the material rather than skimming.

Find real-world CVEs

For each OWASP category, search the National Vulnerability Database at nvd.nist.gov for CVEs tagged with the corresponding CWE identifier. For example, SQL Injection maps to CWE-89, and Cross-Site Scripting maps to CWE-79. Read two or three CVE entries per category, paying attention to the CVSS score, the affected software, and the attack vector. Real CVEs ground abstract vulnerability categories in concrete, exploited weaknesses and help you recognize similar patterns during your own assessments.

Download the OWASP Testing Guide

Download the OWASP Web Security Testing Guide (WSTG) from owasp.org/www-project-web-security-testing-guide/ — it is available as a PDF and as a web-based document. The WSTG provides detailed, step-by-step testing procedures for every vulnerability class in the Top 10 and many more. Skim the table of contents to understand its structure: it is organized by test category (OTG-INFO, OTG-INPVAL, etc.) with each test having a defined objective, test steps, and expected results. This guide will be your primary reference throughout the rest of this course.

Set up DVWA

DVWA (Damn Vulnerable Web Application) is a deliberately insecure PHP application designed for security training. Install it on your Metasploitable VM (it is pre-installed) or set it up separately using Docker with 'docker run --rm -it -p 80:80 vulnerables/web-dvwa'. Access DVWA in your browser at http://<target-ip>/dvwa and log in with admin/password. Set the security level to Low in the DVWA Security settings to start — this disables input validation and makes vulnerabilities easy to trigger, which is ideal for learning the fundamentals before moving to harder levels.

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