Cross Site Request Forgery protection¶

How to use it¶

To enable CSRF protection for your views, follow these steps:

1. Add the middleware 'django.middleware.csrf.CsrfViewMiddleware' to your list of middleware classes, MIDDLEWARE_CLASSES. (It should come before any view middleware that assume that CSRF attacks have been dealt with.)

   Alternatively, you can use the decorator csrf_protect() on particular views you want to protect (see below).

2. In any template that uses a POST form, use the csrf_token tag inside the <form> element if the form is for an internal URL, e.g.:

   <form action="." method="post">{% csrf_token %}
   

   This should not be done for POST forms that target external URLs, since that would cause the CSRF token to be leaked, leading to a vulnerability.

3. In the corresponding view functions, ensure that the 'django.core.context_processors.csrf' context processor is being used. Usually, this can be done in one of two ways:

   1. Use RequestContext, which always uses 'django.core.context_processors.csrf' (no matter what your TEMPLATE_CONTEXT_PROCESSORS setting). If you are using generic views or contrib apps, you are covered already, since these apps use RequestContext throughout.

   2. Manually import and use the processor to generate the CSRF token and add it to the template context. e.g.:

      from django.core.context_processors import csrf
      from django.shortcuts import render_to_response
      
      def my_view(request):
          c = {}
          c.update(csrf(request))
          # ... view code here
          return render_to_response("a_template.html", c)
      

      You may want to write your own render_to_response() wrapper that takes care of this step for you.

The utility script extras/csrf_migration_helper.py (located in the Django distribution, but not installed) can help to automate the finding of code and templates that may need these steps. It contains full help on how to use it.

// using jQuery
function getCookie(name) {
    var cookieValue = null;
    if (document.cookie && document.cookie != '') {
        var cookies = document.cookie.split(';');
        for (var i = 0; i < cookies.length; i++) {
            var cookie = jQuery.trim(cookies[i]);
            // Does this cookie string begin with the name we want?
            if (cookie.substring(0, name.length + 1) == (name + '=')) {
                cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
                break;
            }
        }
    }
    return cookieValue;
}
var csrftoken = getCookie('csrftoken');

var csrftoken = $.cookie('csrftoken');

function csrfSafeMethod(method) {
    // these HTTP methods do not require CSRF protection
    return (/^(GET|HEAD|OPTIONS|TRACE)$/.test(method));
}
function sameOrigin(url) {
    // test that a given url is a same-origin URL
    // url could be relative or scheme relative or absolute
    var host = document.location.host; // host + port
    var protocol = document.location.protocol;
    var sr_origin = '//' + host;
    var origin = protocol + sr_origin;
    // Allow absolute or scheme relative URLs to same origin
    return (url == origin || url.slice(0, origin.length + 1) == origin + '/') ||
        (url == sr_origin || url.slice(0, sr_origin.length + 1) == sr_origin + '/') ||
        // or any other URL that isn't scheme relative or absolute i.e relative.
        !(/^(\/\/|http:|https:).*/.test(url));
}
$.ajaxSetup({
    beforeSend: function(xhr, settings) {
        if (!csrfSafeMethod(settings.type) && sameOrigin(settings.url)) {
            // Send the token to same-origin, relative URLs only.
            // Send the token only if the method warrants CSRF protection
            // Using the CSRFToken value acquired earlier
            xhr.setRequestHeader("X-CSRFToken", csrftoken);
        }
    }
});

function csrfSafeMethod(method) {
    // these HTTP methods do not require CSRF protection
    return (/^(GET|HEAD|OPTIONS|TRACE)$/.test(method));
}
$.ajaxSetup({
    crossDomain: false, // obviates need for sameOrigin test
    beforeSend: function(xhr, settings) {
        if (!csrfSafeMethod(settings.type)) {
            xhr.setRequestHeader("X-CSRFToken", csrftoken);
        }
    }
});

<div style="display:none">
    <input type="hidden" name="csrfmiddlewaretoken" value="$csrf_token"/>
</div>

Rejected requests¶

By default, a ‘403 Forbidden’ response is sent to the user if an incoming request fails the checks performed by CsrfViewMiddleware. This should usually only be seen when there is a genuine Cross Site Request Forgery, or when, due to a programming error, the CSRF token has not been included with a POST form.

The error page, however, is not very friendly, so you may want to provide your own view for handling this condition. To do this, simply set the CSRF_FAILURE_VIEW setting.

How it works¶

The CSRF protection is based on the following things:

1. A CSRF cookie that is set to a random value (a session independent nonce, as it is called), which other sites will not have access to.

   This cookie is set by CsrfViewMiddleware. It is meant to be permanent, but since there is no way to set a cookie that never expires, it is sent with every response that has called django.middleware.csrf.get_token() (the function used internally to retrieve the CSRF token).

2. A hidden form field with the name ‘csrfmiddlewaretoken’ present in all outgoing POST forms. The value of this field is the value of the CSRF cookie.

   This part is done by the template tag.

3. For all incoming requests that are not using HTTP GET, HEAD, OPTIONS or TRACE, a CSRF cookie must be present, and the ‘csrfmiddlewaretoken’ field must be present and correct. If it isn’t, the user will get a 403 error.

   This check is done by CsrfViewMiddleware.

4. In addition, for HTTPS requests, strict referer checking is done by CsrfViewMiddleware. This is necessary to address a Man-In-The-Middle attack that is possible under HTTPS when using a session independent nonce, due to the fact that HTTP ‘Set-Cookie’ headers are (unfortunately) accepted by clients that are talking to a site under HTTPS. (Referer checking is not done for HTTP requests because the presence of the Referer header is not reliable enough under HTTP.)

This ensures that only forms that have originated from your Web site can be used to POST data back.

It deliberately ignores GET requests (and other requests that are defined as ‘safe’ by RFC 2616). These requests ought never to have any potentially dangerous side effects , and so a CSRF attack with a GET request ought to be harmless. RFC 2616 defines POST, PUT and DELETE as ‘unsafe’, and all other methods are assumed to be unsafe, for maximum protection.

Caching¶

If the csrf_token template tag is used by a template (or the get_token function is called some other way), CsrfViewMiddleware will add a cookie and a Vary: Cookie header to the response. This means that the middleware will play well with the cache middleware if it is used as instructed (UpdateCacheMiddleware goes before all other middleware).

However, if you use cache decorators on individual views, the CSRF middleware will not yet have been able to set the Vary header or the CSRF cookie, and the response will be cached without either one. In this case, on any views that will require a CSRF token to be inserted you should use the django.views.decorators.csrf.csrf_protect() decorator first:

from django.views.decorators.cache import cache_page
from django.views.decorators.csrf import csrf_protect

@cache_page(60 * 15)
@csrf_protect
def my_view(request):
    # ...

Testing¶

The CsrfViewMiddleware will usually be a big hindrance to testing view functions, due to the need for the CSRF token which must be sent with every POST request. For this reason, Django’s HTTP client for tests has been modified to set a flag on requests which relaxes the middleware and the csrf_protect decorator so that they no longer rejects requests. In every other respect (e.g. sending cookies etc.), they behave the same.

If, for some reason, you want the test client to perform CSRF checks, you can create an instance of the test client that enforces CSRF checks:

>>> from django.test import Client
>>> csrf_client = Client(enforce_csrf_checks=True)

Limitations¶

Subdomains within a site will be able to set cookies on the client for the whole domain. By setting the cookie and using a corresponding token, subdomains will be able to circumvent the CSRF protection. The only way to avoid this is to ensure that subdomains are controlled by trusted users (or, are at least unable to set cookies). Note that even without CSRF, there are other vulnerabilities, such as session fixation, that make giving subdomains to untrusted parties a bad idea, and these vulnerabilities cannot easily be fixed with current browsers.

Edge cases¶

Certain views can have unusual requirements that mean they don’t fit the normal pattern envisaged here. A number of utilities can be useful in these situations. The scenarios they might be needed in are described in the following section.

from django.views.decorators.csrf import csrf_exempt, csrf_protect

@csrf_exempt
def my_view(request):

    @csrf_protect
    def protected_path(request):
        do_something()

    if some_condition():
       return protected_path(request)
    else:
       do_something_else()

Contrib and reusable apps¶

Because it is possible for the developer to turn off the CsrfViewMiddleware, all relevant views in contrib apps use the csrf_protect decorator to ensure the security of these applications against CSRF. It is recommended that the developers of other reusable apps that want the same guarantees also use the csrf_protect decorator on their views.

Settings¶

A number of settings can be used to control Django’s CSRF behavior.

def csrf_failure(request, reason="")