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"""
Cross Site Request Forgery Middleware.
This module provides a middleware that implements protection
against request forgeries from other sites.
"""
from django.conf import settings
from django.http import HttpResponseForbidden
import md5
import re
import itertools
_ERROR_MSG = '<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"><body><h1>403 Forbidden</h1><p>Cross Site Request Forgery detected. Request aborted.</p></body></html>'
_POST_FORM_RE = \
re.compile(r'(<form\W[^>]*\bmethod=(\'|"|)POST(\'|"|)\b[^>]*>)', re.IGNORECASE)
_HTML_TYPES = ('text/html', 'application/xhtml+xml')
def _make_token(session_id):
return md5.new(settings.SECRET_KEY + session_id).hexdigest()
class CsrfMiddleware(object):
"""Django middleware that adds protection against Cross Site
Request Forgeries by adding hidden form fields to POST forms and
checking requests for the correct value.
In the list of middlewares, SessionMiddleware is required, and must come
after this middleware. CsrfMiddleWare must come after compression
middleware.
If a session ID cookie is present, it is hashed with the SECRET_KEY
setting to create an authentication token. This token is added to all
outgoing POST forms and is expected on all incoming POST requests that
have a session ID cookie.
If you are setting cookies directly, instead of using Django's session
framework, this middleware will not work.
"""
def process_request(self, request):
if request.POST:
try:
session_id = request.COOKIES[settings.SESSION_COOKIE_NAME]
except KeyError:
# No session, no check required
return None
csrf_token = _make_token(session_id)
# check incoming token
try:
request_csrf_token = request.POST['csrfmiddlewaretoken']
except KeyError:
return HttpResponseForbidden(_ERROR_MSG)
if request_csrf_token != csrf_token:
return HttpResponseForbidden(_ERROR_MSG)
return None
def process_response(self, request, response):
csrf_token = None
try:
cookie = response.cookies[settings.SESSION_COOKIE_NAME]
csrf_token = _make_token(cookie.value)
except KeyError:
# No outgoing cookie to set session, but
# a session might already exist.
try:
session_id = request.COOKIES[settings.SESSION_COOKIE_NAME]
csrf_token = _make_token(session_id)
except KeyError:
# no incoming or outgoing cookie
pass
if csrf_token is not None and \
response['Content-Type'].split(';')[0] in _HTML_TYPES:
# ensure we don't add the 'id' attribute twice (HTML validity)
idattributes = itertools.chain(("id='csrfmiddlewaretoken'",),
itertools.repeat(''))
def add_csrf_field(match):
"""Returns the matched <form> tag plus the added <input> element"""
return match.group() + "<div style='display:none;'>" + \
"<input type='hidden' " + idattributes.next() + \
" name='csrfmiddlewaretoken' value='" + csrf_token + \
"' /></div>"
# Modify any POST forms
response.content = _POST_FORM_RE.sub(add_csrf_field, response.content)
return response
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