Source code for django.middleware.csrf

"""
Cross Site Request Forgery Middleware.

This module provides a middleware that implements protection
against request forgeries from other sites.
"""
from __future__ import unicode_literals

import logging
import re

from django.conf import settings
from django.core.urlresolvers import get_callable
from django.utils.cache import patch_vary_headers
from django.utils.crypto import constant_time_compare, get_random_string
from django.utils.encoding import force_text
from django.utils.http import is_same_domain
from django.utils.six.moves.urllib.parse import urlparse

logger = logging.getLogger('django.request')

REASON_NO_REFERER = "Referer checking failed - no Referer."
REASON_BAD_REFERER = "Referer checking failed - %s does not match any trusted origins."
REASON_NO_CSRF_COOKIE = "CSRF cookie not set."
REASON_BAD_TOKEN = "CSRF token missing or incorrect."
REASON_MALFORMED_REFERER = "Referer checking failed - Referer is malformed."
REASON_INSECURE_REFERER = "Referer checking failed - Referer is insecure while host is secure."

CSRF_KEY_LENGTH = 32


def _get_failure_view():
    """
    Returns the view to be used for CSRF rejections
    """
    return get_callable(settings.CSRF_FAILURE_VIEW)


def _get_new_csrf_key():
    return get_random_string(CSRF_KEY_LENGTH)


def get_token(request):
    """
    Returns the CSRF token required for a POST form. The token is an
    alphanumeric value. A new token is created if one is not already set.

    A side effect of calling this function is to make the csrf_protect
    decorator and the CsrfViewMiddleware add a CSRF cookie and a 'Vary: Cookie'
    header to the outgoing response.  For this reason, you may need to use this
    function lazily, as is done by the csrf context processor.
    """
    if "CSRF_COOKIE" not in request.META:
        request.META["CSRF_COOKIE"] = _get_new_csrf_key()
    request.META["CSRF_COOKIE_USED"] = True
    return request.META["CSRF_COOKIE"]


def rotate_token(request):
    """
    Changes the CSRF token in use for a request - should be done on login
    for security purposes.
    """
    request.META.update({
        "CSRF_COOKIE_USED": True,
        "CSRF_COOKIE": _get_new_csrf_key(),
    })


def _sanitize_token(token):
    # Allow only alphanum
    if len(token) > CSRF_KEY_LENGTH:
        return _get_new_csrf_key()
    token = re.sub('[^a-zA-Z0-9]+', '', force_text(token))
    if token == "":
        # In case the cookie has been truncated to nothing at some point.
        return _get_new_csrf_key()
    return token


[docs]class CsrfViewMiddleware(object): """ Middleware that requires a present and correct csrfmiddlewaretoken for POST requests that have a CSRF cookie, and sets an outgoing CSRF cookie. This middleware should be used in conjunction with the csrf_token template tag. """ # The _accept and _reject methods currently only exist for the sake of the # requires_csrf_token decorator. def _accept(self, request): # Avoid checking the request twice by adding a custom attribute to # request. This will be relevant when both decorator and middleware # are used. request.csrf_processing_done = True return None def _reject(self, request, reason): logger.warning('Forbidden (%s): %s', reason, request.path, extra={ 'status_code': 403, 'request': request, } ) return _get_failure_view()(request, reason=reason) def process_view(self, request, callback, callback_args, callback_kwargs): if getattr(request, 'csrf_processing_done', False): return None try: csrf_token = _sanitize_token( request.COOKIES[settings.CSRF_COOKIE_NAME]) # Use same token next time request.META['CSRF_COOKIE'] = csrf_token except KeyError: csrf_token = None # Wait until request.META["CSRF_COOKIE"] has been manipulated before # bailing out, so that get_token still works if getattr(callback, 'csrf_exempt', False): return None # Assume that anything not defined as 'safe' by RFC7231 needs protection if request.method not in ('GET', 'HEAD', 'OPTIONS', 'TRACE'): if getattr(request, '_dont_enforce_csrf_checks', False): # Mechanism to turn off CSRF checks for test suite. # It comes after the creation of CSRF cookies, so that # everything else continues to work exactly the same # (e.g. cookies are sent, etc.), but before any # branches that call reject(). return self._accept(request) if request.is_secure(): # Suppose user visits http://example.com/ # An active network attacker (man-in-the-middle, MITM) sends a # POST form that targets https://example.com/detonate-bomb/ and # submits it via JavaScript. # # The attacker will need to provide a CSRF cookie and token, but # that's no problem for a MITM and the session-independent # nonce we're using. So the MITM can circumvent the CSRF # protection. This is true for any HTTP connection, but anyone # using HTTPS expects better! For this reason, for # https://example.com/ we need additional protection that treats # http://example.com/ as completely untrusted. Under HTTPS, # Barth et al. found that the Referer header is missing for # same-domain requests in only about 0.2% of cases or less, so # we can use strict Referer checking. referer = force_text( request.META.get('HTTP_REFERER'), strings_only=True, errors='replace' ) if referer is None: return self._reject(request, REASON_NO_REFERER) referer = urlparse(referer) # Make sure we have a valid URL for Referer. if '' in (referer.scheme, referer.netloc): return self._reject(request, REASON_MALFORMED_REFERER) # Ensure that our Referer is also secure. if referer.scheme != 'https': return self._reject(request, REASON_INSECURE_REFERER) # If there isn't a CSRF_COOKIE_DOMAIN, assume we need an exact # match on host:port. If not, obey the cookie rules. if settings.CSRF_COOKIE_DOMAIN is None: # request.get_host() includes the port. good_referer = request.get_host() else: good_referer = settings.CSRF_COOKIE_DOMAIN server_port = request.get_port() if server_port not in ('443', '80'): good_referer = '%s:%s' % (good_referer, server_port) # Here we generate a list of all acceptable HTTP referers, # including the current host since that has been validated # upstream. good_hosts = list(settings.CSRF_TRUSTED_ORIGINS) good_hosts.append(good_referer) if not any(is_same_domain(referer.netloc, host) for host in good_hosts): reason = REASON_BAD_REFERER % referer.geturl() return self._reject(request, reason) if csrf_token is None: # No CSRF cookie. For POST requests, we insist on a CSRF cookie, # and in this way we can avoid all CSRF attacks, including login # CSRF. return self._reject(request, REASON_NO_CSRF_COOKIE) # Check non-cookie token for match. request_csrf_token = "" if request.method == "POST": try: request_csrf_token = request.POST.get('csrfmiddlewaretoken', '') except IOError: # Handle a broken connection before we've completed reading # the POST data. process_view shouldn't raise any # exceptions, so we'll ignore and serve the user a 403 # (assuming they're still listening, which they probably # aren't because of the error). pass if request_csrf_token == "": # Fall back to X-CSRFToken, to make things easier for AJAX, # and possible for PUT/DELETE. request_csrf_token = request.META.get(settings.CSRF_HEADER_NAME, '') if not constant_time_compare(request_csrf_token, csrf_token): return self._reject(request, REASON_BAD_TOKEN) return self._accept(request) def process_response(self, request, response): if getattr(response, 'csrf_processing_done', False): return response if not request.META.get("CSRF_COOKIE_USED", False): return response # Set the CSRF cookie even if it's already set, so we renew # the expiry timer. response.set_cookie(settings.CSRF_COOKIE_NAME, request.META["CSRF_COOKIE"], max_age=settings.CSRF_COOKIE_AGE, domain=settings.CSRF_COOKIE_DOMAIN, path=settings.CSRF_COOKIE_PATH, secure=settings.CSRF_COOKIE_SECURE, httponly=settings.CSRF_COOKIE_HTTPONLY ) # Content varies with the CSRF cookie, so set the Vary header. patch_vary_headers(response, ('Cookie',)) response.csrf_processing_done = True return response
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