Fixed #25334 -- Provided a way to allow cross-origin unsafe requests over HTTPS.

Added the CSRF_TRUSTED_ORIGINS setting which contains a list of other
domains that are included during the CSRF Referer header verification
for secure (HTTPS) requests.

7 files changed, 48 insertions, 5 deletions

diff --git a/django/conf/global_settings.py b/django/conf/global_settings.py
index 280bfeb167..6b759d8454 100644
--- a/django/conf/global_settings.py
+++ b/django/conf/global_settings.py
@@ -558,6 +558,7 @@ CSRF_COOKIE_PATH = '/'
 CSRF_COOKIE_SECURE = False
 CSRF_COOKIE_HTTPONLY = False
 CSRF_HEADER_NAME = 'HTTP_X_CSRFTOKEN'
+CSRF_TRUSTED_ORIGINS = []
 
 ############
 # MESSAGES #
diff --git a/django/middleware/csrf.py b/django/middleware/csrf.py
index 6d16a92bf5..dee5bb1d93 100644
--- a/django/middleware/csrf.py
+++ b/django/middleware/csrf.py
@@ -19,7 +19,7 @@ from django.utils.http import same_origin
 logger = logging.getLogger('django.request')
 
 REASON_NO_REFERER = "Referer checking failed - no Referer."
-REASON_BAD_REFERER = "Referer checking failed - %s does not match %s."
+REASON_BAD_REFERER = "Referer checking failed - %s does not match any trusted origins."
 REASON_NO_CSRF_COOKIE = "CSRF cookie not set."
 REASON_BAD_TOKEN = "CSRF token missing or incorrect."
 
@@ -154,10 +154,15 @@ class CsrfViewMiddleware(object):
                 if referer is None:
                     return self._reject(request, REASON_NO_REFERER)
 
+                # Here we generate a list of all acceptable HTTP referers,
+                # including the current host since that has been validated
+                # upstream.
+                good_hosts = list(settings.CSRF_TRUSTED_ORIGINS)
                 # Note that request.get_host() includes the port.
-                good_referer = 'https://%s/' % request.get_host()
-                if not same_origin(referer, good_referer):
-                    reason = REASON_BAD_REFERER % (referer, good_referer)
+                good_hosts.append(request.get_host())
+                good_referers = ['https://{0}/'.format(host) for host in good_hosts]
+                if not any(same_origin(referer, host) for host in good_referers):
+                    reason = REASON_BAD_REFERER % referer
                     return self._reject(request, reason)
 
             if csrf_token is None:
diff --git a/docs/ref/csrf.txt b/docs/ref/csrf.txt
index 590990571f..ba24339a78 100644
--- a/docs/ref/csrf.txt
+++ b/docs/ref/csrf.txt
@@ -257,7 +257,8 @@ The CSRF protection is based on the following things:
    due to the fact that HTTP 'Set-Cookie' headers are (unfortunately) accepted
    by clients that are talking to a site under HTTPS.  (Referer checking is not
    done for HTTP requests because the presence of the Referer header is not
-   reliable enough under HTTP.)
+   reliable enough under HTTP.) Expanding the accepted referers beyond the
+   current host can be done with the :setting:`CSRF_TRUSTED_ORIGINS` setting.
 
 This ensures that only forms that have originated from your Web site can be used
 to POST data back.
@@ -460,3 +461,4 @@ A number of settings can be used to control Django's CSRF behavior:
 * :setting:`CSRF_COOKIE_SECURE`
 * :setting:`CSRF_FAILURE_VIEW`
 * :setting:`CSRF_HEADER_NAME`
+* :setting:`CSRF_TRUSTED_ORIGINS`
diff --git a/docs/ref/settings.txt b/docs/ref/settings.txt
index 217f54281d..ed5ac98947 100644
--- a/docs/ref/settings.txt
+++ b/docs/ref/settings.txt
@@ -428,6 +428,23 @@ any hyphens with underscores, and adding an ``'HTTP_'`` prefix to the name.
 For example, if your client sends a ``'X-XSRF-TOKEN'`` header, the setting
 should be ``'HTTP_X_XSRF_TOKEN'``.
 
+.. setting:: CSRF_TRUSTED_ORIGINS
+
+CSRF_TRUSTED_ORIGINS
+--------------------
+
+.. versionadded:: 1.9
+
+Default: ``[]`` (Empty list)
+
+A list of hosts which are trusted origins for unsafe requests (e.g. ``POST``).
+For a :meth:`secure <django.http.HttpRequest.is_secure>` unsafe
+request, Django's CSRF protection requires that the request have a ``Referer``
+header that matches the origin present in the ``Host`` header. This prevents,
+for example, a ``POST`` request from ``subdomain.example.com`` from succeeding
+against ``api.example.com``. If you need cross-origin unsafe requests over
+HTTPS, continuing the example, add ``"subdomain.example.com"`` to this list.
+
 .. setting:: DATABASES
 
 DATABASES
@@ -3374,6 +3391,7 @@ Security
   * :setting:`CSRF_COOKIE_SECURE`
   * :setting:`CSRF_FAILURE_VIEW`
   * :setting:`CSRF_HEADER_NAME`
+  * :setting:`CSRF_TRUSTED_ORIGINS`
 
 * :setting:`SECRET_KEY`
 * :setting:`X_FRAME_OPTIONS`
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index 5c0e3b613c..cf7909057b 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -484,6 +484,9 @@ CSRF
 * The request header's name used for CSRF authentication can be customized
   with :setting:`CSRF_HEADER_NAME`.
 
+* The new :setting:`CSRF_TRUSTED_ORIGINS` setting provides a way to allow
+  cross-origin unsafe requests (e.g. ``POST``) over HTTPS.
+
 Signals
 ^^^^^^^
 
diff --git a/docs/spelling_wordlist b/docs/spelling_wordlist
index 691ab2f4ef..1edaa68d49 100644
--- a/docs/spelling_wordlist
+++ b/docs/spelling_wordlist
@@ -644,6 +644,7 @@ refactoring
 refactorings
 refactors
 referer
+referers
 reflow
 regex
 regexes
diff --git a/tests/csrf_tests/tests.py b/tests/csrf_tests/tests.py
index 2d347ccdde..aaa9a6969a 100644
--- a/tests/csrf_tests/tests.py
+++ b/tests/csrf_tests/tests.py
@@ -352,6 +352,19 @@ class CsrfViewMiddlewareTest(SimpleTestCase):
         req2 = CsrfViewMiddleware().process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
+    @override_settings(ALLOWED_HOSTS=['www.example.com'], CSRF_TRUSTED_ORIGINS=['dashboard.example.com'])
+    def test_https_csrf_trusted_origin_allowed(self):
+        """
+        A POST HTTPS request with a referer added to the CSRF_TRUSTED_ORIGINS
+        setting is accepted.
+        """
+        req = self._get_POST_request_with_token()
+        req._is_secure_override = True
+        req.META['HTTP_HOST'] = 'www.example.com'
+        req.META['HTTP_REFERER'] = 'https://dashboard.example.com'
+        req2 = CsrfViewMiddleware().process_view(req, post_form_view, (), {})
+        self.assertIsNone(req2)
+
     def test_ensures_csrf_cookie_no_middleware(self):
         """
         Tests that ensures_csrf_cookie decorator fulfils its promise