266 lines
12 KiB
Python
266 lines
12 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.safestring import mark_safe
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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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# 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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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.
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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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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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def process_view(self, request, callback, callback_args, callback_kwargs):
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if getattr(callback, 'csrf_exempt', False):
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return None
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if getattr(request, 'csrf_processing_done', False):
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return None
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reject = lambda s: _get_failure_view()(request, reason=s)
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def accept():
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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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# 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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request.META["CSRF_COOKIE"] = 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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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 accept()
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if request.is_ajax():
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# .is_ajax() is based on the presence of X-Requested-With. In
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# the context of a browser, this can only be sent if using
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# XmlHttpRequest. Browsers implement careful policies for
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# XmlHttpRequest:
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#
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# * Normally, only same-domain requests are allowed.
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#
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# * Some browsers (e.g. Firefox 3.5 and later) relax this
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# carefully:
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#
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# * if it is a 'simple' GET or POST request (which can
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# include no custom headers), it is allowed to be cross
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# domain. These requests will not be recognized as AJAX.
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#
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# * if a 'preflight' check with the server confirms that the
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# server is expecting and allows the request, cross domain
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# requests even with custom headers are allowed. These
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# requests will be recognized as AJAX, but can only get
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# through when the developer has specifically opted in to
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# allowing the cross-domain POST request.
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#
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# So in all cases, it is safe to allow these requests through.
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return accept()
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if request.is_secure():
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# Strict referer checking for HTTPS
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referer = request.META.get('HTTP_REFERER')
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if referer is None:
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return reject("Referer checking failed - 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. This might be too strict.
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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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return reject("Referer checking failed - %s does not match %s." %
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(referer, good_referer))
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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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return reject("No CSRF or session 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', None)
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if 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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return reject("CSRF cookie not set.")
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else:
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return reject("CSRF token missing or incorrect.")
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return accept()
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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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PendingDeprecationWarning
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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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