man CGI::Untaint () - process CGI input parameters


CGI::Untaint - process CGI input parameters


  use CGI::Untaint;

  my $q = new CGI;
  my $handler = CGI::Untaint->new( $q->Vars );
  my $handler2 = CGI::Untaint->new({
        INCLUDE_PATH => 'My::Untaint',
  }, $apr->parms);

  my $name     = $handler->extract(-as_printable => 'name');
  my $homepage = $handler->extract(-as_url => 'homepage');

  my $postcode = $handler->extract(-as_postcode => 'address6');

  # Create your own handler...

  package MyRecipes::CGI::Untaint::legal_age;
  use base 'CGI::Untaint::integer';
  sub is_valid { 
    shift->value > 21;

  package main;
  my $age = $handler->extract(-as_legal_age => 'age');


Dealing with large web based applications with multiple forms is a minefield. It's often hard enough to ensure you validate all your input at all, without having to worry about doing it in a consistent manner. If any of the validation rules change, you often have to alter them in many different places. And, if you want to operate taint-safe, then you're just adding even more headaches.

This module provides a simple, convenient, abstracted and extensible manner for validating and untainting the input from web forms.

You simply create a handler with a hash of your parameters (usually CW$q->Vars), and then iterate over the fields you wish to extract, performing whatever validations you choose. The resulting variable is guaranteed not only to be valid, but also untainted.



  my $handler  = CGI::Untaint->new( $q->Vars );
  my $handler2 = CGI::Untaint->new({
        INCLUDE_PATH => 'My::Untaint',
  }, $apr->parms);

The simplest way to contruct an input handler is to pass a hash of parameters (usually CW$q->Vars) to new(). Each parameter will then be able to be extracted later by calling an extract() method on it.

However, you may also pass a leading reference to a hash of configuration variables.

Currently the only such variable supported is 'INCLUDE_PATH', which allows you to specify a local path in which to find extraction handlers. See LOCAL EXTRACTION HANDLERS.



  my $homepage = $handler->extract(-as_url => 'homepage');
  my $state = $handler->extract(-as_us_state => 'address4');
  my $state = $handler->extract(-as_like_us_state => 'address4');

Once you have constructed your Input Handler, you call the 'extract' method on each piece of data with which you are concerned.

The takes an -as_whatever flag to state what type of data you require. This will check that the input value correctly matches the required specification, and return an untainted value. It will then call the is_valid() method, where applicable, to ensure that this doesn't just _look_ like a valid value, but actually is one.

If you want to skip this stage, then you can call -as_like_whatever which will perform the untainting but not the validation.


  my $error = $handler->error;

If the validation failed, this will return the reason why.


As well as as the handlers supplied with this module for extracting data, you may also create your own. In general these should inherit from 'CGI::Untaint::object', and must provide an '_untaint_re' method which returns a compiled regular expression, suitably bracketed such that CW$1 will return the untainted value required.

e.g. if you often extract single digit variables, you could create

  package My::Untaint::digit;

  use base 'CGI::Untaint::object';

  sub _untaint_re { qr/^(\d)$/ }


You should specify the path 'My::Untaint' in the INCLUDE_PATH configuration option. (See new() above.)

When extract() is called CGI::Untaint will also check to see if you have an is_valid() method also, and if so will run this against the value extracted from the regular expression (available as CW$self->value).

If this returns a true value, then the extracted value will be returned, otherwise we return undef.

is_valid() can also modify the value being returned, by assigning CW$self->value($new_value)

e.g. in the above example, if you sometimes need to ensure that the digit extracted is prime, you would supply:

  sub is_valid { (1 x shift->value) !~ /^1?$|^(11+?)\1+$/ };

Now, when users call extract(), it will also check that the value is valid(), i.e. prime:

  my $number = $handler->extract(-as_digit => 'value');

A user wishing to skip the validation, but still ensure untainting can call

  my $number = $handler->extract(-as_like_digit => 'value');


If you create your own local handlers, then you may wish to explore Test::CGI::Untaint, available from the CPAN. This makes it very easy to write tests for your handler. (Thanks to Profero Ltd.)


This package comes with the following simplistic handlers:

  printable  - a printable string
  integer    - an integer
  hex        - a hexadecimal number (as a string)

To really make this work for you you either need to write, or download from CPAN, other handlers. Some of the handlers available on CPAN include:

  asin         - an Amazon ID
  boolean      - boolean value
  country      - a country code or name
  creditcard   - a credit card number
  date         - a date (into a Date::Simple)
  datetime     - a date (into a DateTime)
  email        - an email address
  hostname     - a DNS host name
  html         - sanitized HTML
  ipaddress    - an IP address
  isbn         - an ISBN
  uk_postcode  - a UK Postcode
  url          - a URL
  zipcode      - a US zipcode


None known yet.


CGI. perlsec. Test::CGI::Untaint.


Tony Bowden


Please direct all correspondence regarding this module to:


Copyright (C) 2001-2005 Tony Bowden. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.