[Hone Your Ninja Skill] Whitelist filter bypass ("URL")

By YGN Ethical Hacker Group -
http://honeyourskills.ninja/target/web/data_restriction/?url=whitelist-filter-bypass-url.php

In input validation, whitelisting approach is said to be better than blacklisting one.  Yet non-robust implementation in whitelisting  could also allow attacker to bypass your defense.

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