Locking Down Ruby

$SAFE = 2 unless $SAFE > 2

Ruby has a handy security feature that tracks whether variables are tainted. A tainted variable is one that has received its data from some sort of external source (such as a CGI form field or an IO stream) or from copying the contents of another tainted variable. Then certain methods that are considered dangerous will refuse to run if they receive data marked as tainted. These features are turned on and off at varying levels through the use of the $SAFE variable.