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Application & OT Security · Foundational

Allowlist Validation

Input validation that accepts only values matching a known-good pattern or set and rejects everything else.

Definition

Also called positive validation, allowlisting is stronger than denylisting because it does not depend on predicting every malicious variant. It is ideal for structured data such as IDs, dates, enumerations and country codes.

Example

A sort parameter is accepted only if it is one of 'name', 'date' or 'price'.

Exam tip

Allowlist (positive) validation is preferred over denylist (negative) validation.

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