Input Validation — Trust Nothing, Verify Everything
Client vs server validation, Zod for schema validation, and common input validation patterns
Every security vulnerability we've covered in this module has one thing in common: they exploit the gap between what your app expects to receive and what an attacker actually sends.
SQL injection sends SQL commands where you expected a search term. XSS sends script tags where you expected a comment. Brute force sends thousands of passwords where you expected one.
Input validation is the practice of checking that what you receive matches what you expect — before you do anything with it. It's the single most effective defense against the widest range of attacks.
The Golden Rule
Never trust data from the client. Validate everything on the server.
This sounds obvious, but here's why developers get it wrong: they think client-side validation is security. It's not. It's user experie
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