Web security encompasses the practices and controls that protect web applications from attacks that threaten confidentiality, integrity, and availability. In the modern threat landscape, where applications process sensitive data and connect users across untrusted networks, defending against injection attacks, authentication bypasses, and misconfigurations is no longer optional—it's a fundamental requirement. Understanding how attackers exploit common vulnerabilities like XSS, CSRF, and SQL injection, and knowing the concrete patterns and headers that prevent them, equips developers to build systems that resist both automated scanning and targeted exploitation.