Preventing Cross-Site Scripting (XSS) in Modern Web Apps

Cross-Site Scripting (XSS) remains one of the most prevalent and dangerous vulnerabilities in web development, allowing attackers to hijack user sessions and steal sensitive data. Understanding how to build secure applications from the ground up is essential for any modern developer. This text-based course guides you through the core mechanisms of XSS and equips you with the practical defense strategies needed to secure your frontend and backend code. You will learn to identify vulnerable entry points and implement industry-standard defenses. What you'll learn: - Understand the fundamental types of XSS, including Stored, Reflected, and DOM-based attacks. - Apply contextual HTML, CSS, and JavaScript encoding to safely render user-supplied data. - Implement secure input handling and validation strategies to filter malicious payloads. - Configure a robust Content Security Policy (CSP) to mitigate the impact of injection vulnerabilities. - Leverage modern framework-level protections and sanitization libraries to automate defenses. The course begins with foundational security concepts and terminology, explaining how browsers interpret untrusted data. You will then progress through written code examples, step-by-step mitigation strategies, and practical text-based exercises designed to reinforce secure coding habits. This course is designed for junior developers, web designers, and security beginners who want to write safer code, with no prior security experience required. Start reading today to master the essential techniques of web application defense.