Web Vulnerabilities
Input Validation
Also: input checking
Checking that incoming data matches what the program expects (type, length, range, allowed values) before using it.
In more detail
The strongest form is an allowlist: accept only values you know are good, such as a number between 1 and 100, or a name from a fixed list. Rejecting known-bad patterns instead (a denylist) tends to miss variations. Validation reduces risk but is not a substitute for using safe interfaces, such as parameterized queries.