.. _using-csrf:

===================================

How to use Django's CSRF protection

===================================

To take advantage of CSRF protection in your views, follow these steps:

#. The CSRF middleware is activated by default in the :setting:`MIDDLEWARE`

   setting. If you override that setting, remember that

   ``'django.middleware.csrf.CsrfViewMiddleware'`` should come before any view

   middleware that assume that CSRF attacks have been dealt with.

   If you disabled it, which is not recommended, you can use

   :func:`~django.views.decorators.csrf.csrf_protect` on particular views

   you want to protect (see below).

#. In any template that uses a POST form, use the :ttag:`csrf_token` tag inside

   the ``<form>`` element if the form is for an internal URL, e.g.:

   .. code-block:: html+django

       <form 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.

#. In the corresponding view functions, ensure that

   :class:`~django.template.RequestContext` is used to render the response so

   that ``{% csrf_token %}`` will work properly. If you're using the

   :func:`~django.shortcuts.render` function, generic views, or contrib apps,

   you are covered already since these all use ``RequestContext``.

.. _csrf-ajax:

Using CSRF protection with AJAX

===============================

While the above method can be used for AJAX POST requests, it has some

inconveniences: you have to remember to pass the CSRF token in as POST data with

every POST request. For this reason, there is an alternative method: on each

XMLHttpRequest, set a custom ``X-CSRFToken`` header (as specified by the

:setting:`CSRF_HEADER_NAME` setting) to the value of the CSRF token. This is

often easier because many JavaScript frameworks provide hooks that allow

headers to be set on every request.

First, you must get the CSRF token. How to do that depends on whether or not

the :setting:`CSRF_USE_SESSIONS` and :setting:`CSRF_COOKIE_HTTPONLY` settings

are enabled.

.. _acquiring-csrf-token-from-cookie:

Acquiring the token if :setting:`CSRF_USE_SESSIONS` and :setting:`CSRF_COOKIE_HTTPONLY` are ``False``

-----------------------------------------------------------------------------------------------------

The recommended source for the token is the ``csrftoken`` cookie, which will be

set if you've enabled CSRF protection for your views as outlined above.

The CSRF token cookie is named ``csrftoken`` by default, but you can control

the cookie name via the :setting:`CSRF_COOKIE_NAME` setting.

You can acquire the token like this:

.. code-block:: javascript

    function getCookie(name) {

        let cookieValue = null;

        if (document.cookie && document.cookie !== '') {

            const cookies = document.cookie.split(';');

            for (let i = 0; i < cookies.length; i++) {

                const cookie = cookies[i].trim();

                // 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;

    }

    const csrftoken = getCookie('csrftoken');

The above code could be simplified by using the `JavaScript Cookie library

<https://github.com/js-cookie/js-cookie/>`_ to replace ``getCookie``:

.. code-block:: javascript

    const csrftoken = Cookies.get('csrftoken');

.. note::

    The CSRF token is also present in the DOM in a masked form, but only if

    explicitly included using :ttag:`csrf_token` in a template. The cookie

    contains the canonical, unmasked token. The

    :class:`~django.middleware.csrf.CsrfViewMiddleware` will accept either.

    However, in order to protect against `BREACH`_ attacks, it's recommended to

    use a masked token.

.. warning::

    If your view is not rendering a template containing the :ttag:`csrf_token`

    template tag, Django might not set the CSRF token cookie. This is common in

    cases where forms are dynamically added to the page. To address this case,

    Django provides a view decorator which forces setting of the cookie:

    :func:`~django.views.decorators.csrf.ensure_csrf_cookie`.

.. _BREACH: https://www.breachattack.com/

.. _acquiring-csrf-token-from-html:

Acquiring the token if :setting:`CSRF_USE_SESSIONS` or :setting:`CSRF_COOKIE_HTTPONLY` is ``True``

--------------------------------------------------------------------------------------------------

If you activate :setting:`CSRF_USE_SESSIONS` or

:setting:`CSRF_COOKIE_HTTPONLY`, you must include the CSRF token in your HTML

and read the token from the DOM with JavaScript:

.. code-block:: html+django

    {% csrf_token %}

    <script>

    const csrftoken = document.querySelector('[name=csrfmiddlewaretoken]').value;

    </script>

Setting the token on the AJAX request

-------------------------------------

Finally, you'll need to set the header on your AJAX request. Using the

`fetch()`_ API:

.. code-block:: javascript

    const request = new Request(

        /* URL */,

        {

            method: 'POST',

            headers: {'X-CSRFToken': csrftoken},

            mode: 'same-origin' // Do not send CSRF token to another domain.

        }

    );

    fetch(request).then(function(response) {

        // ...

    });

.. _fetch(): https://developer.mozilla.org/en-US/docs/Web/API/fetch

Using CSRF protection in Jinja2 templates

=========================================

Django's :class:`~django.template.backends.jinja2.Jinja2` template backend

adds ``{{ csrf_input }}`` to the context of all templates which is equivalent

to ``{% csrf_token %}`` in the Django template language. For example:

.. code-block:: html+jinja

    <form method="post">{{ csrf_input }}

Using the decorator method

==========================

Rather than adding ``CsrfViewMiddleware`` as a blanket protection, you can use

the :func:`~django.views.decorators.csrf.csrf_protect` decorator, which has

exactly the same functionality, on particular views that need the protection.

It must be used **both** on views that insert the CSRF token in the output, and

on those that accept the POST form data. (These are often the same view

function, but not always).

Use of the decorator by itself is **not recommended**, since if you forget to

use it, you will have a security hole. The 'belt and braces' strategy of using

both is fine, and will incur minimal overhead.

.. _csrf-rejected-requests:

Handling 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, set the

:setting:`CSRF_FAILURE_VIEW` setting.

CSRF failures are logged as warnings to the :ref:`django.security.csrf

<django-security-logger>` logger.

Using CSRF protection with caching

==================================

If the :ttag:`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

:func:`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):

      ...

If you are using class-based views, you can refer to :ref:`Decorating

class-based views<decorating-class-based-views>`.

Testing and CSRF protection

===========================

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)

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.

Disabling CSRF protection for just a few views

----------------------------------------------

Most views requires CSRF protection, but a few do not.

Solution: rather than disabling the middleware and applying ``csrf_protect`` to

all the views that need it, enable the middleware and use

:func:`~django.views.decorators.csrf.csrf_exempt`.

Setting the token when ``CsrfViewMiddleware.process_view()`` is not used

------------------------------------------------------------------------

There are cases when ``CsrfViewMiddleware.process_view`` may not have run

before your view is run - 404 and 500 handlers, for example - but you still

need the CSRF token in a form.

Solution: use :func:`~django.views.decorators.csrf.requires_csrf_token`

Including the CSRF token in an unprotected view

-----------------------------------------------

There may be some views that are unprotected and have been exempted by

``csrf_exempt``, but still need to include the CSRF token.

Solution: use :func:`~django.views.decorators.csrf.csrf_exempt` followed by

:func:`~django.views.decorators.csrf.requires_csrf_token`. (i.e. ``requires_csrf_token``

should be the innermost decorator).

Protecting a view for only one path

-----------------------------------

A view needs CSRF protection under one set of conditions only, and mustn't have

it for the rest of the time.

Solution: use :func:`~django.views.decorators.csrf.csrf_exempt` for the whole

view function, and :func:`~django.views.decorators.csrf.csrf_protect` for the

path within it that needs protection. Example::

    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()

Protecting a page that uses AJAX without an HTML form

-----------------------------------------------------

A page makes a POST request via AJAX, and the page does not have an HTML form

with a :ttag:`csrf_token` that would cause the required CSRF cookie to be sent.

Solution: use :func:`~django.views.decorators.csrf.ensure_csrf_cookie` on the

view that sends the page.

CSRF protection in reusable applications

========================================

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.