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Refs #28592 -- Created a new CSRF how-to document.

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@ -0,0 +1,309 @@
.. _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:
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: http://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:
Handle 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.
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.
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.

1
docs/howto/index.txt
View File

@ -11,6 +11,7 @@ you quickly accomplish common tasks.
:maxdepth: 1
auth-remote-user
csrf
custom-management-commands
custom-model-fields
custom-lookups

350
docs/ref/csrf.txt
View File

@ -16,215 +16,10 @@ a site with someone else's credentials, is also covered.
The first defense against CSRF attacks is to ensure that GET requests (and other
'safe' methods, as defined by :rfc:`7231#section-4.2.1`) are side effect free.
Requests via 'unsafe' methods, such as POST, PUT, and DELETE, can then be
protected by following the steps below.
protected by the steps outlined in :ref:`using-csrf`.
.. _Cross Site Request Forgeries: https://www.squarefree.com/securitytips/web-developers.html#CSRF
.. _using-csrf:
How to use it
=============
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:
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`.
.. _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 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 }}
The decorator method
--------------------
.. module:: django.views.decorators.csrf
Rather than adding ``CsrfViewMiddleware`` as a blanket protection, you can use
the ``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.
.. function:: csrf_protect(view)
Decorator that provides the protection of ``CsrfViewMiddleware`` to a view.
Usage::
from django.shortcuts import render
from django.views.decorators.csrf import csrf_protect
@csrf_protect
def my_view(request):
c = {}
# ...
return render(request, "a_template.html", c)
If you are using class-based views, you can refer to
:ref:`Decorating class-based views<decorating-class-based-views>`.
.. _csrf-rejected-requests:
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.
.. _how-csrf-works:
How it works
@ -328,49 +123,6 @@ vulnerability allows and much worse).
.. _Origin header: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Origin
.. _disable the referer: https://www.w3.org/TR/referrer-policy/#referrer-policy-delivery
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
=======
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)
.. _csrf-limitations:
Limitations
@ -384,16 +136,10 @@ 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.
Utilities
---------
=========
.. module:: django.views.decorators.csrf
The examples below assume you are using function-based views. If you
are working with class-based views, you can refer to :ref:`Decorating
@ -411,6 +157,21 @@ class-based views<decorating-class-based-views>`.
def my_view(request):
return HttpResponse('Hello world')
.. function:: csrf_protect(view)
Decorator that provides the protection of ``CsrfViewMiddleware`` to a view.
Usage::
from django.shortcuts import render
from django.views.decorators.csrf import csrf_protect
@csrf_protect
def my_view(request):
c = {}
# ...
return render(request, "a_template.html", c)
.. function:: requires_csrf_token(view)
Normally the :ttag:`csrf_token` template tag will not work if
@ -434,79 +195,6 @@ class-based views<decorating-class-based-views>`.
This decorator forces a view to send the CSRF cookie.
Scenarios
---------
CSRF protection should be disabled 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`.
CsrfViewMiddleware.process_view 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`
Unprotected view needs the CSRF token
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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).
View needs protection for 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()
Page uses AJAX without any 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.
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
========