oracular (3) CGI::Application::Plugin::ProtectCSRF.3pm.gz
NAME
CGI::Application::Plugin::ProtectCSRF - generate and verify anti-CSRF tickets
VERSION
1.01
SYNPSIS
use Your::App;
use base qw(CGI::Application);
use CGI::Application::Plugin::Session; # mandatory !!
use CGI::Application::Plugin::ProtectCSRF;
sub input_form : PublishCSRFID {
my $self = shift;
do_something();
}
sub finish : ProtectCSRF {
my $self = shift;
$self->clear_csrf_id;
do_something();
}
DESCRIPTION
CGI::Application::Plugin::ProtectCSRF provides tools to protect forms in CGI::Application web
applications from CSRF attacks. Run mode handlers may be declared with the "PublishCSFRID" or
"ProtectCSFR" attributes. The former should usually be applied to a run mode, whose HTML includes a
"form" tag. In this case a ticket is generated and stored in the session during a prerun callback and a
"hidden" control field, publishing the ticket, is added to the form during a postrun callback. Conversely
the "ProtectCSRF" attribute should normally be applied to the corresponding run modes that process data
from a submitted form. A prerun callback checks for the hidden field and checks that it matches the
ticket saved in the session. If the check fails the page is redirected to a customizable error page. On
success the form processing run mode should use the "clear_csrf_id" method, so that subsequent calls to
forms from that session will generate fresh tickets.
ACTION
PublishCSRFID
Run modes declared with the "PublishCSRFID" attribute, take the following actions:
- generate CSRF ticket and store it in the session;
- generate the form as per the module code;
- add a hidden element to the form publishing the CSRF ticket.
# publish CSRF ticket
sub input_form : PublishCSRFID {
my $self = shift;
return <<HTML;
<form action="foo" method="post">
<input type="text" name="name">
<input type="submit" value="submit!">
<input type="hidden" name="rm" value="finish">
</form>
HTML
}
# display html source
<form action="foo" method="post">
<input type="hidden" name="_csrf_id" value="random string" /> <- insert hidden field
<input type="text" name="name">
<input type="submit" value="submit!">
<input type="hidden" name="rm" value="finish">
</form>
ProtectCSRF
Run modes declared with the "ProtectCSRF" attribute, take the following actions:
- verify that the submitted CSRF ticket matches the ticket saved in the session. If there is any sort of
issue with the ticket the page is redirected to a customizable error page;
- the form is processed as per the module code;
- the form should call the "clear_csfr_id" method so that subsequent forms generate fresh tickets. The
code does not do this because if the form validation fails it might be best to retain the same ticket.
sub finish : ProtectCSRF {
my $self = shift;
# required! Unless forms and their processing are tightly
# coupled by clearing the ticket between invocations,
# the meaning of the ticket is lost.
$self->clear_csrf_id;
# The processing that you want to perform (DB processing etc)
do_something();
}
METHOD
csrf_id
This method returns the CSRF ticket saved in the session.
Example:
sub input_form : PublishCSRFID {
my $self = shift;
my $csrf_id = $self->csrf_id;
do_something();
}
protect_csrf_config
This method initializes the ProtectCSRF state using any configuration options that were passed to it. The
available options are:
csrf_error_status - The HTTP status code that would be set on the CSRF error page if a CSRF attack is
identified. It defaults to 200.
csrf_error_mode - The CGI::Application runmode name. This defaults to "_csrf_error".
csrf_error_tmpl - The HTML displayed in the event of a CSRF attack being detected in the form of a
scalarref or filepath or filehandle. One may consider HTML::Template for inspiration on thse formats. The
default is $CSRF_ERROR_TMPL which is a scalarref.
csrf_error_tmpl_param - A hashref of parameters to be placed in the above template. See HTML::Template.
csrf_id - The name of the session parameter used to store the CSRF ticket.This defaults to "_csrf_id".
csrf_post_only - If set non-POST requests to a run mode which is protected by this module would be
rejected. By default this is 0.
Example:
sub cgiapp_init {
my $self = shift;
$self->tmpl_path("/path/to/template");
$self->protect_csrf_config(
csrf_error_status => 403, # change forbidden
csrf_error_tmpl => "csrf_error.tmpl",
csrf_error_tmpl_param => { TITLE => "CSRF ERROR", MESSAGE => "your access is csrf!"},
csrf_id => "ticket_id",
csrf_post_only => 1
);
}
# csrf_error.tmpl
<html><head><title><TMPL_VAR NAME=TITLE ESCAPE=HTML></title></head>
<body>
<h1>CSRF Error</h1>
<span style="color: red"><TMPL_VAR NAME=MESSAGE ESCAPE=HTML></span>
</body>
</html>
clear_csrf_id
This method clears the CSFR ticket. This should be done during the processing of a form request.
Example :
sub cgiapp_init {
my $self = shift;
$self->protect_csrf_config;
}
sub input {
my $self = shift;
do_something(). # input form display..
}
sub confirm : PublishCSRFID {
my $self = shift;
do_something(). # publish csrf_id and input check and confirm display..
}
sub complete : ProtectCSRF {
my $self = shift;
$self->clear_csrf_id(1); # clear csrf_id for CSRF protect
do_something(); # DB insert etc..
}
CALLBACK
_publish_csrf_id
prerun callback
_csrf_forbidden
prerun callback
_add_csrf_id
postrun callback
CAUTION
This module should not be seen as a panacea for all web security issues. The user should fully
understand and act on all security threats his application may face, including whether this module is an
adequate and useful tool.
SEE ALSO
Attribute::Handlers, Carp, CGI::Application, CGI::Application::Plugin::Session, Digest::SHA, Exporter,
HTML::TokeParser, HTML::Template
AUTHOR
Akira Horimoto <kurt0027@gmail.com>
COPYRIGHT
Copyright (C) 2006 - 2008 Akira Horimoto
This module is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.