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Application & OT Security · Foundational

Input Validation

Checking that all untrusted input conforms to expected type, length, format and range before it is processed.

Definition

Validation should occur on the server side (client-side checks are easily bypassed), use allowlists where possible, and happen after canonicalization. It reduces many vulnerability classes but is not a substitute for context-specific defenses like parameterized queries and output encoding.

Example

A ZIP code field accepts only five digits, validated with an anchored regular expression on the server.

Exam tip

Client-side validation is for usability only; server-side validation is the security control.

Don't confuse it with

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