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module ActionController #:nodoc:
class InvalidAuthenticityToken < ActionControllerError #:nodoc:
end
module RequestForgeryProtection
def self.included(base)
base.class_eval do
class_inheritable_accessor :request_forgery_protection_options
self.request_forgery_protection_options = {}
helper_method :form_authenticity_token
helper_method :protect_against_forgery?
end
base.extend(ClassMethods)
end
module ClassMethods
# Protect a controller's actions from CSRF attacks by ensuring that all forms are coming from the current web application, not
# a forged link from another site. This is done by embedding a token based on the session (which an attacker wouldn't know) in
# all forms and Ajax requests generated by Rails and then verifying the authenticity of that token in the controller. Only
# HTML/JavaScript requests are checked, so this will not protect your XML API (presumably you'll have a different authentication
# scheme there anyway). Also, GET requests are not protected as these should be indempotent anyway.
#
# You turn this on with the #protect_from_forgery method, which will perform the check and raise
# an ActionController::InvalidAuthenticityToken if the token doesn't match what was expected. And it will add
# a _authenticity_token parameter to all forms that are automatically generated by Rails. You can customize the error message
# given through public/422.html.
#
# Learn more about CSRF (Cross-Site Request Forgery) attacks:
#
# * http://isc.sans.org/diary.html?storyid=1750
# * http://en.wikipedia.org/wiki/Cross-site_request_forgery
#
# Keep in mind, this is NOT a silver-bullet, plug 'n' play, warm security blanket for your rails application.
# There are a few guidelines you should follow:
#
# * Keep your GET requests safe and idempotent. More reading material:
# * http://www.xml.com/pub/a/2002/04/24/deviant.html
# * http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
# * Make sure the session cookies that Rails creates are non-persistent. Check in Firefox and look for "Expires: at end of session"
#
# If you need to construct a request yourself, but still want to take advantage of forgery protection, you can grab the
# authenticity_token using the form_authenticity_token helper method and make it part of the parameters yourself.
#
# Example:
#
# class FooController < ApplicationController
# # uses the cookie session store (then you don't need a separate :secret)
# protect_from_forgery :except => :index
#
# # uses one of the other session stores that uses a session_id value.
# protect_from_forgery :secret => 'my-little-pony', :except => :index
#
# # you can disable csrf protection on controller-by-controller basis:
# skip_before_filter :verify_authenticity_token
# end
#
# Valid Options:
#
# * <tt>:only/:except</tt> - passed to the before_filter call. Set which actions are verified.
# * <tt>:secret</tt> - Custom salt used to generate the form_authenticity_token.
# Leave this off if you are using the cookie session store.
# * <tt>:digest</tt> - Message digest used for hashing. Defaults to 'SHA1'
def protect_from_forgery(options = {})
self.request_forgery_protection_token ||= :authenticity_token
before_filter :verify_authenticity_token, :only => options.delete(:only), :except => options.delete(:except)
request_forgery_protection_options.update(options)
end
end
protected
# The actual before_filter that is used. Modify this to change how you handle unverified requests.
def verify_authenticity_token
verified_request? || raise(ActionController::InvalidAuthenticityToken)
end
# Returns true or false if a request is verified. Checks:
#
# * is the format restricted? By default, only HTML and AJAX requests are checked.
# * is it a GET request? Gets should be safe and idempotent
# * Does the form_authenticity_token match the given _token value from the params?
def verified_request?
!protect_against_forgery? ||
request.method == :get ||
!verifiable_request_format? ||
form_authenticity_token == params[request_forgery_protection_token]
end
def verifiable_request_format?
request.format.html? || request.format.js?
end
# Sets the token value for the current session. Pass a :secret option in #protect_from_forgery to add a custom salt to the hash.
def form_authenticity_token
@form_authenticity_token ||= if request_forgery_protection_options[:secret]
authenticity_token_from_session_id
elsif session.respond_to?(:dbman) && session.dbman.respond_to?(:generate_digest)
authenticity_token_from_cookie_session
elsif session.nil?
raise InvalidAuthenticityToken, "Request Forgery Protection requires a valid session. Use #allow_forgery_protection to disable it, or use a valid session."
else
raise InvalidAuthenticityToken, "No :secret given to the #protect_from_forgery call. Set that or use a session store capable of generating its own keys (Cookie Session Store)."
end
end
# Generates a unique digest using the session_id and the CSRF secret.
def authenticity_token_from_session_id
key = if request_forgery_protection_options[:secret].respond_to?(:call)
request_forgery_protection_options[:secret].call(@session)
else
request_forgery_protection_options[:secret]
end
digest = request_forgery_protection_options[:digest] ||= 'SHA1'
OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(digest), key.to_s, session.session_id.to_s)
end
# No secret was given, so assume this is a cookie session store.
def authenticity_token_from_cookie_session
session[:csrf_id] ||= CGI::Session.generate_unique_id
session.dbman.generate_digest(session[:csrf_id])
end
def protect_against_forgery?
allow_forgery_protection && request_forgery_protection_token
end
end
end
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