++ed by:
Chisel

NAME

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

VERSION

version 0.0.4

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',
            cookie_options          => {},
            cookie_expiry_seconds   => (3 * 60 * 60),
            token_per_request       => 0,
            meta_tag                => undef,
            header_name             => undef,
            blocked                 => sub {
                                        return [ $status, $headers, $body ]
                                    },
        ;
        $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.

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

Extra cookie options to be set with the cookie. This is useful for things like setting HttpOnly to tell the browser to only send it with HTTP requests, and Secure on the cookie to force the cookie to only be sent on SSL requests.

    builder {
        enable 'XSRFBlock', cookie_options => { secure => 1, httponly => 1 };
    }
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.

header_name (default: undef)

If this is set, use the value as the name of the response heaer that the token can be sent in. This is useful for non-browser based submissions; e.g. Javascript AJAX requests.

blocked (default: undef)

If this is set it should be a PSGI application that is returned instead of the default HTTP_FORBIDDEN(403) and text/plain response.

This could be useful if you'd like to perform some action that's more in keeping with your application - e.g. return a styled error page.

ERRORS

The module emits various errors based on the cause of the XSRF detected. The messages will be of the form XSRF detected [reason]

form field missing

The request was submitted but there was no value submitted in the form field specified by <C$self->parameter_name> [default: xsrf_token]

xsrf token missing

The application has been configured to accept an 'X-' header and no token value was found in either the header or a suitable form field. [default: undef]

There is no cookie with the name specified by $self-cookie_name> [default: PSGI-XSRF-Token]

invalid token

The cookie token and form value were both submitted correctly but the values do not match.

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.

FURTHER READING

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.

CONTRIBUTORS

  • Chisel <chisel.wright@net-a-porter.com>

  • Chisel Wright <chisel@chizography.net>

  • Matthew Ryall <matt.ryall@gmail.com>

  • Sebastian Willert <willert@gmail.com>

  • William Wolf <throughnothing@gmail.com>




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