Input Validation Security: Server-Side Rules
The principles of secure input validation: allowlists over denylists, validation vs sanitization, and where validation must happen.
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Tags: security, web, validation
Input Validation vs Sanitization: Security Best Practices Input validation and input sanitization are two distinct strategies for handling untrusted data, and confusing them leads to either over-blocking legitimate input or under-protecting against attacks. Validation rejects bad input; sanitization cleans it. The right strategy depends on context, and often both are needed. The Core Distinction Validation: Check if input meets expected criteria. If it does not, reject it with an error. The input is never used. Sanitization: Transform potentially dangerous input into a safe form. The sanitized version is used. Allowlist vs Blocklist Allowlist (whitelist): Define what is acceptable. Accept only inputs matching the allowlist; reject everything else. Blocklist (blacklist): Define what is…
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