My understanding of the taint flag as implemented in Perl is that it is very much a whitelist. All user input is born tainted and much be verified clean before

My understanding of the taint flag as implemented in Perl is that it is very much a whitelist. All user input is born tainted and much be verified clean before the flag is removed. It's possible to screw this up by verifying too much, but that's an overly-expansive whitelist problem, not a blacklist that isn't restrictive enough.