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""" |
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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 re |
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import itertools |
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from django.conf import settings |
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from django.http import HttpResponseForbidden |
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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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_ERROR_MSG = mark_safe('<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>') |
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_POST_FORM_RE = \ |
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re.compile(r'(<form\W[^>]*\bmethod=(\'|"|)POST(\'|"|)\b[^>]*>)', re.IGNORECASE) |
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_HTML_TYPES = ('text/html', 'application/xhtml+xml') |
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def _make_token(session_id): |
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return md5_constructor(settings.SECRET_KEY + session_id).hexdigest() |
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class CsrfMiddleware(object): |
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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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In the list of middlewares, SessionMiddleware is required, and must come |
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after this middleware. CsrfMiddleWare must come after compression |
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middleware. |
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If a session ID cookie is present, it is hashed with the SECRET_KEY |
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setting to create an authentication token. This token is added to all |
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outgoing POST forms and is expected on all incoming POST requests that |
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have a session ID cookie. |
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If you are setting cookies directly, instead of using Django's session |
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framework, this middleware will not work. |
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""" |
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def process_request(self, request): |
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if request.method == 'POST': |
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try: |
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session_id = request.COOKIES[settings.SESSION_COOKIE_NAME] |
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except KeyError: |
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# No session, no check required |
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return None |
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csrf_token = _make_token(session_id) |
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# check incoming token |
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try: |
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request_csrf_token = request.POST['csrfmiddlewaretoken'] |
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except KeyError: |
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return HttpResponseForbidden(_ERROR_MSG) |
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if request_csrf_token != csrf_token: |
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return HttpResponseForbidden(_ERROR_MSG) |
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return None |
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def process_response(self, request, response): |
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csrf_token = None |
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try: |
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cookie = response.cookies[settings.SESSION_COOKIE_NAME] |
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csrf_token = _make_token(cookie.value) |
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except KeyError: |
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# No outgoing cookie to set session, but |
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# a session might already exist. |
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try: |
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session_id = request.COOKIES[settings.SESSION_COOKIE_NAME] |
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csrf_token = _make_token(session_id) |
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except KeyError: |
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# no incoming or outgoing cookie |
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pass |
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|
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if csrf_token is not None and \ |
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response['Content-Type'].split(';')[0] in _HTML_TYPES: |
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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 = _POST_FORM_RE.sub(add_csrf_field, response.content) |
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return response |
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