Input Validation and Output Encoding
Validate all inputs on the server side, encode outputs in the correct context, and prevent injection.
Why Input Validation Matters
Injection vulnerabilities — SQL, command, LDAP, XPath, and more — arise when untrusted input is interpreted as code. Input validation ensures data conforms to expected types, lengths, and formats before it is processed, stored, or returned.
Allowlist vs Denylist Validation
Allowlist (whitelist) validation defines what IS acceptable: only alphanumeric characters, only integers in range 1-100, only valid email formats. Denylist (blacklist) tries to block known bad inputs and is always incomplete. Prefer allowlists.
All lessons in this course
- Input Validation and Output Encoding
- Secure Dependency Management
- OWASP ASVS: Application Security Verification Standard
- Secure Code Review Techniques