Input Validation & XSS Prevention The Universal Truth of Web Security Never trust user input. This is the foundational principle of web security. Every major breach can be traced back to input validation failures: - SQL Injection - Equifax (147 million records) - XSS - British Airways (380,000 transactions, £20M fine) - Command Injection - Countless others According to OWASP, injection vulnerabilities are consistently the #1 or #2 threat to web applications. Input validation is not optional—it's existential. Understanding XSS (Cross-Site Scripting) The Attack Attacker enters in a bio field: W…