# untaint parameters
for( keys %params )
{
    ( display_message( $messages{error} ) && exit )
        unless ref($valid_params{$_}) eq 'Regexp';

    my $temp = $params{$_};            ### <--- added this variable

    if( $temp =~ /$valid_params{$_}/ ) ### <--- changed this line
    {
        $params{$_} = $1;
    }
    else
    {
        display_message( $messages{error} ) && exit;
    }
}