Controller actions are protected from Cross-Site Request Forgery (CSRF) attacks by including a token in the rendered html for your application. This token is stored as a random string in the session, to which an attacker does not have access. When a request reaches your application, Rails verifies the received token with the token in the session. Only HTML and 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 idempotent.
CSRF protection is turned on with the protect_from_forgery
method, which checks the token and resets the session if it doesn't
match what was expected. A call to this method is generated for new Rails
applications by default. You can customize the error message by editing
public/422.html.
The token parameter is named authenticity_token
by default.
The name and value of this token must be added to every layout that renders
forms by including csrf_meta_tags
in the html
head
.
Learn more about CSRF attacks and securing your application in the Ruby on Rails Security Guide.
The form's authenticity parameter. Override to provide your own.
# File lib/action_controller/metal/request_forgery_protection.rb, line 105 def form_authenticity_param params[request_forgery_protection_token] end
Sets the token value for the current session.
# File lib/action_controller/metal/request_forgery_protection.rb, line 100 def form_authenticity_token session[:_csrf_token] ||= SecureRandom.base64(32) end
This is the method that defines the application behavior when a request is found to be unverified. By default, Rails resets the session when it finds an unverified request.
# File lib/action_controller/metal/request_forgery_protection.rb, line 84 def handle_unverified_request reset_session end
# File lib/action_controller/metal/request_forgery_protection.rb, line 109 def protect_against_forgery? allow_forgery_protection end
Returns true or false if a request is verified. Checks:
is it a GET request? Gets should be safe and idempotent
Does the #form_authenticity_token match the given token value from the params?
Does the X-CSRF-Token header match the #form_authenticity_token
# File lib/action_controller/metal/request_forgery_protection.rb, line 93 def verified_request? !protect_against_forgery? || request.get? || form_authenticity_token == params[request_forgery_protection_token] || form_authenticity_token == request.headers['X-CSRF-Token'] end
The actual before_filter that is used. Modify this to change how you handle unverified requests.
# File lib/action_controller/metal/request_forgery_protection.rb, line 75 def verify_authenticity_token unless verified_request? logger.warn "WARNING: Can't verify CSRF token authenticity" if logger handle_unverified_request end end