218 lines
8.7 KiB
Python
218 lines
8.7 KiB
Python
"""
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Cross Site Request Forgery Middleware.
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This module provides a middleware that implements protection
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against request forgeries from other sites.
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"""
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from __future__ import unicode_literals
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import hashlib
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import re
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import random
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from django.conf import settings
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from django.core.urlresolvers import get_callable
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from django.utils.cache import patch_vary_headers
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from django.utils.encoding import force_text
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from django.utils.http import same_origin
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from django.utils.log import getLogger
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from django.utils.crypto import constant_time_compare, get_random_string
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logger = getLogger('django.request')
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REASON_NO_REFERER = "Referer checking failed - no Referer."
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REASON_BAD_REFERER = "Referer checking failed - %s does not match %s."
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REASON_NO_CSRF_COOKIE = "CSRF cookie not set."
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REASON_BAD_TOKEN = "CSRF token missing or incorrect."
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CSRF_KEY_LENGTH = 32
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def _get_failure_view():
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"""
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Returns the view to be used for CSRF rejections
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"""
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return get_callable(settings.CSRF_FAILURE_VIEW)
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def _get_new_csrf_key():
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return get_random_string(CSRF_KEY_LENGTH)
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def get_token(request):
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"""
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Returns the the CSRF token required for a POST form. The token is an
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alphanumeric value.
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A side effect of calling this function is to make the the csrf_protect
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decorator and the CsrfViewMiddleware add a CSRF cookie and a 'Vary: Cookie'
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header to the outgoing response. For this reason, you may need to use this
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function lazily, as is done by the csrf context processor.
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"""
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request.META["CSRF_COOKIE_USED"] = True
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return request.META.get("CSRF_COOKIE", None)
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def _sanitize_token(token):
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# Allow only alphanum
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if len(token) > CSRF_KEY_LENGTH:
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return _get_new_csrf_key()
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token = re.sub('[^a-zA-Z0-9]+', '', force_text(token))
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if token == "":
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# In case the cookie has been truncated to nothing at some point.
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return _get_new_csrf_key()
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return token
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class CsrfViewMiddleware(object):
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"""
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Middleware that requires a present and correct csrfmiddlewaretoken
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for POST requests that have a CSRF cookie, and sets an outgoing
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CSRF cookie.
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This middleware should be used in conjunction with the csrf_token template
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tag.
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"""
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# The _accept and _reject methods currently only exist for the sake of the
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# requires_csrf_token decorator.
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def _accept(self, request):
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# Avoid checking the request twice by adding a custom attribute to
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# request. This will be relevant when both decorator and middleware
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# are used.
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request.csrf_processing_done = True
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return None
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def _reject(self, request, reason):
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return _get_failure_view()(request, reason=reason)
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def process_view(self, request, callback, callback_args, callback_kwargs):
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if getattr(request, 'csrf_processing_done', False):
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return None
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try:
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csrf_token = _sanitize_token(
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request.COOKIES[settings.CSRF_COOKIE_NAME])
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# Use same token next time
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request.META['CSRF_COOKIE'] = csrf_token
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except KeyError:
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csrf_token = None
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# Generate token and store it in the request, so it's
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# available to the view.
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request.META["CSRF_COOKIE"] = _get_new_csrf_key()
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# Wait until request.META["CSRF_COOKIE"] has been manipulated before
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# bailing out, so that get_token still works
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if getattr(callback, 'csrf_exempt', False):
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return None
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# Assume that anything not defined as 'safe' by RC2616 needs protection
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if request.method not in ('GET', 'HEAD', 'OPTIONS', 'TRACE'):
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if getattr(request, '_dont_enforce_csrf_checks', False):
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# Mechanism to turn off CSRF checks for test suite.
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# It comes after the creation of CSRF cookies, so that
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# everything else continues to work exactly the same
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# (e.g. cookies are sent, etc.), but before any
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# branches that call reject().
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return self._accept(request)
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if request.is_secure():
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# Suppose user visits http://example.com/
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# An active network attacker (man-in-the-middle, MITM) sends a
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# POST form that targets https://example.com/detonate-bomb/ and
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# submits it via JavaScript.
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#
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# The attacker will need to provide a CSRF cookie and token, but
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# that's no problem for a MITM and the session-independent
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# nonce we're using. So the MITM can circumvent the CSRF
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# protection. This is true for any HTTP connection, but anyone
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# using HTTPS expects better! For this reason, for
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# https://example.com/ we need additional protection that treats
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# http://example.com/ as completely untrusted. Under HTTPS,
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# Barth et al. found that the Referer header is missing for
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# same-domain requests in only about 0.2% of cases or less, so
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# we can use strict Referer checking.
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referer = request.META.get('HTTP_REFERER')
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if referer is None:
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logger.warning('Forbidden (%s): %s',
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REASON_NO_REFERER, request.path,
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extra={
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'status_code': 403,
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'request': request,
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}
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)
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return self._reject(request, REASON_NO_REFERER)
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# Note that request.get_host() includes the port.
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good_referer = 'https://%s/' % request.get_host()
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if not same_origin(referer, good_referer):
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reason = REASON_BAD_REFERER % (referer, good_referer)
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logger.warning('Forbidden (%s): %s', reason, request.path,
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extra={
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'status_code': 403,
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'request': request,
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}
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)
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return self._reject(request, reason)
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if csrf_token is None:
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# No CSRF cookie. For POST requests, we insist on a CSRF cookie,
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# and in this way we can avoid all CSRF attacks, including login
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# CSRF.
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logger.warning('Forbidden (%s): %s',
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REASON_NO_CSRF_COOKIE, request.path,
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extra={
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'status_code': 403,
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'request': request,
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}
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)
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return self._reject(request, REASON_NO_CSRF_COOKIE)
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# Check non-cookie token for match.
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request_csrf_token = ""
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if request.method == "POST":
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request_csrf_token = request.POST.get('csrfmiddlewaretoken', '')
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if request_csrf_token == "":
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# Fall back to X-CSRFToken, to make things easier for AJAX,
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# and possible for PUT/DELETE.
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request_csrf_token = request.META.get('HTTP_X_CSRFTOKEN', '')
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if not constant_time_compare(request_csrf_token, csrf_token):
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logger.warning('Forbidden (%s): %s',
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REASON_BAD_TOKEN, request.path,
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extra={
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'status_code': 403,
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'request': request,
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}
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)
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return self._reject(request, REASON_BAD_TOKEN)
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return self._accept(request)
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def process_response(self, request, response):
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if getattr(response, 'csrf_processing_done', False):
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return response
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# If CSRF_COOKIE is unset, then CsrfViewMiddleware.process_view was
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# never called, probaby because a request middleware returned a response
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# (for example, contrib.auth redirecting to a login page).
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if request.META.get("CSRF_COOKIE") is None:
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return response
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if not request.META.get("CSRF_COOKIE_USED", False):
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return response
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# Set the CSRF cookie even if it's already set, so we renew
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# the expiry timer.
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response.set_cookie(settings.CSRF_COOKIE_NAME,
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request.META["CSRF_COOKIE"],
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max_age = 60 * 60 * 24 * 7 * 52,
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domain=settings.CSRF_COOKIE_DOMAIN,
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path=settings.CSRF_COOKIE_PATH,
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secure=settings.CSRF_COOKIE_SECURE
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)
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# Content varies with the CSRF cookie, so set the Vary header.
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patch_vary_headers(response, ('Cookie',))
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response.csrf_processing_done = True
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return response
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