NAME

Plack::Middleware::XSRFBlock - Block XSRF Attacks with minimal changes to your app

VERSION

version 0.0.0_02

SYNOPSIS

The simplest way to use the plugin is:

use Plack::Builder;

my $app = sub { ... };

builder {
    enable 'XSRFBlock';
    $app;
}

You may also over-ride any, or all of these values:

builder {
    enable 'XSRFBlock',
        parameter_name      => 'xsrf_token',
        cookie_name         => 'PSGI-XSRF-Token',
        token_per_request   => 0,
        meta_tag            => undef,
    ;
    $app;
}

DESCRIPTION

This middleware blocks XSRF. You can use this middleware without any modifications to your application.

OPTIONS

• parameter_name (default: 'xsrf_token')

  The name assigned to the hidden form input containing the token.

• cookie_name (default: 'PSGI-XSRF-Token')

  The name of the cookie used to store the token value.

• token_per_request (default: 0)

  If this is true a new token is assigned for each request made.

  This may make your application more secure, or less susceptible to double-submit issues.

• meta_tag (default: undef)

  If this is set, use the value as the name of the meta tag to add to the head section of output pages.

  This is useful when you are using javascript that requires access to the token value for making AJAX requests.

EXPLANATION

This module is similar in nature and intention to Plack::Middleware::CSRFBlock but implements the xSRF prevention in a different manner.

The solution implemented in this module is based on a CodingHorror article - Preventing CSRF and XSRF Attacks.

The driving comment behind this implementation is from the Felten and Zeller paper:

When a user visits a site, the site should generate a
(cryptographically strong) pseudorandom value and set it as
a cookie on the user's machine. The site should require
every form submission to include this pseudorandom value as
a form value and also as a cookie value. When a POST request
is sent to the site, the request should only be considered
valid if the form value and the cookie value are the same.
When an attacker submits a form on behalf of a user, he can
only modify the values of the form. An attacker cannot read
any data sent from the server or modify cookie values, per
the same-origin policy.  This means that while an attacker
can send any value he wants with the form, he will be unable
to modify or read the value stored in the cookie. Since the
cookie value and the form value must be the same, the
attacker will be unable to successfully submit a form unless
he is able to guess the pseudorandom value.

What's wrong with Plack::Middleware::CSRFBlock?

Plack::Middleware::CSRFBlock is a great module. It does a great job of preventing CSRF behaviour with minimal effort.

However when we tried to use it uses the session to store information - which works well most of the time but can cause issues with session timeouts or removal (for any number of valid reasons) combined with logging (back) in to the application in another tab (so as not to interfere with the current screen/tab state).

Trying to modify the existing module to provide the extra functionality and behaviour we decided worked better for our use seemed too far reaching to try to force into the existing module.

SEE ALSO

Plack::Middleware::CSRFBlock, Plack::Middleware, Plack

AUTHOR

Chisel chisel@chizography.net

COPYRIGHT AND LICENSE

This software is copyright (c) 2013 by Chisel Wright.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.