327 lines
14 KiB
Python
327 lines
14 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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import itertools
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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.hashcompat import md5_constructor
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from django.utils.log import getLogger
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from django.utils.safestring import mark_safe
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from django.utils.crypto import constant_time_compare
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_POST_FORM_RE = \
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re.compile(r'(<form\W[^>]*\bmethod\s*=\s*(\'|"|)POST(\'|"|)\b[^>]*>)', re.IGNORECASE)
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_HTML_TYPES = ('text/html', 'application/xhtml+xml')
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logger = getLogger('django.request')
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# Use the system (hardware-based) random number generator if it exists.
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if hasattr(random, 'SystemRandom'):
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randrange = random.SystemRandom().randrange
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else:
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randrange = random.randrange
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_MAX_CSRF_KEY = 18446744073709551616L # 2 << 63
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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_COOKIE = "No CSRF or session cookie."
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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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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 md5_constructor("%s%s"
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% (randrange(0, _MAX_CSRF_KEY), settings.SECRET_KEY)).hexdigest()
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def _make_legacy_session_token(session_id):
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return md5_constructor(settings.SECRET_KEY + session_id).hexdigest()
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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, and ensure we return a 'str' for the sake of the post
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# processing middleware.
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token = re.sub('[^a-zA-Z0-9]', '', str(token.decode('ascii', 'ignore')))
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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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else:
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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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# If the user doesn't have a CSRF cookie, generate one and store it in the
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# request, so it's available to the view. We'll store it in a cookie when
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# we reach the response.
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try:
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# In case of cookies from untrusted sources, we strip anything
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# dangerous at this point, so that the cookie + token will have the
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# same, sanitized value.
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request.META["CSRF_COOKIE"] = _sanitize_token(request.COOKIES[settings.CSRF_COOKIE_NAME])
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cookie_is_new = False
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except KeyError:
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# No cookie, so create one. This will be sent with the next
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# response.
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request.META["CSRF_COOKIE"] = _get_new_csrf_key()
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# Set a flag to allow us to fall back and allow the session id in
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# place of a CSRF cookie for this request only.
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cookie_is_new = True
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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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if request.method == 'POST':
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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. It comes after
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# the creation of CSRF cookies, so that everything else continues to
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# work exactly the same (e.g. cookies are sent etc), but before the
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# any 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 which 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 is no problem for a MITM and the session independent
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# nonce we are 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' % (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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# The following check ensures that the referer is HTTPS,
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# the domains match and the ports match - the same origin policy.
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good_referer = 'https://%s/' % request.get_host()
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if not referer.startswith(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 the user didn't already have a CSRF cookie, then fall back to
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# the Django 1.1 method (hash of session ID), so a request is not
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# rejected if the form was sent to the user before upgrading to the
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# Django 1.2 method (session independent nonce)
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if cookie_is_new:
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try:
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session_id = request.COOKIES[settings.SESSION_COOKIE_NAME]
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csrf_token = _make_legacy_session_token(session_id)
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except KeyError:
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# No CSRF cookie and no session cookie. For POST requests,
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# we insist on a CSRF cookie, and in this way we can avoid
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# all CSRF attacks, including login CSRF.
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logger.warning('Forbidden (%s): %s' % (REASON_NO_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_COOKIE)
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else:
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csrf_token = request.META["CSRF_COOKIE"]
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# check incoming token
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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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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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if cookie_is_new:
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# probably a problem setting the CSRF cookie
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logger.warning('Forbidden (%s): %s' % (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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else:
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logger.warning('Forbidden (%s): %s' % (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 the expiry timer.
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response.set_cookie(settings.CSRF_COOKIE_NAME,
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request.META["CSRF_COOKIE"], max_age = 60 * 60 * 24 * 7 * 52,
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domain=settings.CSRF_COOKIE_DOMAIN)
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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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class CsrfResponseMiddleware(object):
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"""
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DEPRECATED
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Middleware that post-processes a response to add a csrfmiddlewaretoken.
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This exists for backwards compatibility and as an interim measure until
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applications are converted to using use the csrf_token template tag
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instead. It will be removed in Django 1.4.
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"""
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def __init__(self):
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import warnings
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warnings.warn(
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"CsrfResponseMiddleware and CsrfMiddleware are deprecated; use CsrfViewMiddleware and the template tag instead (see CSRF documentation).",
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DeprecationWarning
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)
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def process_response(self, request, response):
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if getattr(response, 'csrf_exempt', False):
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return response
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if response['Content-Type'].split(';')[0] in _HTML_TYPES:
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csrf_token = get_token(request)
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# If csrf_token is None, we have no token for this request, which probably
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# means that this is a response from a request middleware.
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if csrf_token is None:
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return response
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# ensure we don't add the 'id' attribute twice (HTML validity)
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idattributes = itertools.chain(("id='csrfmiddlewaretoken'",),
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itertools.repeat(''))
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def add_csrf_field(match):
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"""Returns the matched <form> tag plus the added <input> element"""
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return mark_safe(match.group() + "<div style='display:none;'>" + \
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"<input type='hidden' " + idattributes.next() + \
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" name='csrfmiddlewaretoken' value='" + csrf_token + \
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"' /></div>")
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# Modify any POST forms
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response.content, n = _POST_FORM_RE.subn(add_csrf_field, response.content)
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if n > 0:
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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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# Since the content has been modified, any Etag will now be
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# incorrect. We could recalculate, but only if we assume that
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# the Etag was set by CommonMiddleware. The safest thing is just
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# to delete. See bug #9163
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del response['ETag']
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return response
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class CsrfMiddleware(object):
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"""
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Django middleware that adds protection against Cross Site
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Request Forgeries by adding hidden form fields to POST forms and
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checking requests for the correct value.
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CsrfMiddleware uses two middleware, CsrfViewMiddleware and
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CsrfResponseMiddleware, which can be used independently. It is recommended
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to use only CsrfViewMiddleware and use the csrf_token template tag in
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templates for inserting the token.
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"""
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# We can't just inherit from CsrfViewMiddleware and CsrfResponseMiddleware
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# because both have process_response methods.
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def __init__(self):
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self.response_middleware = CsrfResponseMiddleware()
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self.view_middleware = CsrfViewMiddleware()
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def process_response(self, request, resp):
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# We must do the response post-processing first, because that calls
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# get_token(), which triggers a flag saying that the CSRF cookie needs
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# to be sent (done in CsrfViewMiddleware.process_response)
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resp2 = self.response_middleware.process_response(request, resp)
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return self.view_middleware.process_response(request, resp2)
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def process_view(self, request, callback, callback_args, callback_kwargs):
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return self.view_middleware.process_view(request, callback, callback_args,
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callback_kwargs)
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