[1.8.x] Fixed CVE-2016-9014 -- Validated Host header when DEBUG=True.

This is a security fix.

django/http/request.py

@@ -85,12 +85,13 @@ class HttpRequest(object):
             if server_port != ('443' if self.is_secure() else '80'):
                 host = '%s:%s' % (host, server_port)
 
-        # There is no hostname validation when DEBUG=True
+        # Allow variants of localhost if ALLOWED_HOSTS is empty and DEBUG=True.
-        if settings.DEBUG:
+        allowed_hosts = settings.ALLOWED_HOSTS
-            return host
+        if settings.DEBUG and not allowed_hosts:
+            allowed_hosts = ['localhost', '127.0.0.1', '[::1]']
 
         domain, port = split_domain_port(host)
-        if domain and validate_host(domain, settings.ALLOWED_HOSTS):
+        if domain and validate_host(domain, allowed_hosts):
             return host
         else:
             msg = "Invalid HTTP_HOST header: %r." % host

docs/ref/settings.txt

@@ -108,14 +108,18 @@ If the ``Host`` header (or ``X-Forwarded-Host`` if
 list, the :meth:`django.http.HttpRequest.get_host()` method will raise
 :exc:`~django.core.exceptions.SuspiciousOperation`.
 
-When :setting:`DEBUG` is ``True`` or when running tests, host validation is
+When :setting:`DEBUG` is ``True`` and ``ALLOWED_HOSTS`` is empty, the host
-disabled; any host will be accepted. Thus it's usually only necessary to set it
+is validated against ``['localhost', '127.0.0.1', '[::1]']``.
-in production.
 
 This validation only applies via :meth:`~django.http.HttpRequest.get_host()`;
 if your code accesses the ``Host`` header directly from ``request.META`` you
 are bypassing this security protection.
 
+.. versionchanged:: 1.8.16
+
+    In older versions, ``ALLOWED_HOSTS`` wasn't checked if ``DEBUG=True``, but
+    it's now checked to prevent a DNS rebinding attack.
+
 .. setting:: ALLOWED_INCLUDE_ROOTS
 
 ALLOWED_INCLUDE_ROOTS

docs/releases/1.8.16.txt

@@ -19,3 +19,25 @@ the ``manage.py test --keepdb`` option or if the user has an active session
 (such as an attacker's connection).
 
 A randomly generated password is now used for each test run.
+
+DNS rebinding vulnerability when ``DEBUG=True``
+===============================================
+
+Older versions of Django don't validate the ``Host`` header against
+``settings.ALLOWED_HOSTS`` when ``settings.DEBUG=True``. This makes them
+vulnerable to a `DNS rebinding attack
+<http://benmmurphy.github.io/blog/2016/07/11/rails-webconsole-dns-rebinding/>`_.
+
+While Django doesn't ship a module that allows remote code execution, this is
+at least a cross-site scripting vector, which could be quite serious if
+developers load a copy of the production database in development or connect to
+some production services for which there's no development instance, for
+example. If a project uses a package like the ``django-debug-toolbar``, then
+the attacker could execute arbitrary SQL, which could be especially bad if the
+developers connect to the database with a superuser account.
+
+``settings.ALLOWED_HOSTS`` is now validated regardless of ``DEBUG``. For
+convenience, if ``ALLOWED_HOSTS`` is empty and ``DEBUG=True``, the following
+variations of localhost are allowed ``['localhost', '127.0.0.1', '::1']``. If
+your local settings file has your production ``ALLOWED_HOSTS`` value, you must
+now omit it to get those fallback values.

tests/requests/tests.py

@@ -673,21 +673,22 @@ class HostValidationTests(SimpleTestCase):
                 request.get_host()
 
     @override_settings(DEBUG=True, ALLOWED_HOSTS=[])
-    def test_host_validation_disabled_in_debug_mode(self):
+    def test_host_validation_in_debug_mode(self):
-        """If ALLOWED_HOSTS is empty and DEBUG is True, all hosts pass."""
+        """
-        request = HttpRequest()
+        If ALLOWED_HOSTS is empty and DEBUG is True, variants of localhost are
-        request.META = {
+        allowed.
-            'HTTP_HOST': 'example.com',
+        """
-        }
+        valid_hosts = ['localhost', '127.0.0.1', '[::1]']
-        self.assertEqual(request.get_host(), 'example.com')
+        for host in valid_hosts:
+            request = HttpRequest()
+            request.META = {'HTTP_HOST': host}
+            self.assertEqual(request.get_host(), host)
 
-        # Invalid hostnames would normally raise a SuspiciousOperation,
+        # Other hostnames raise a SuspiciousOperation.
-        # but we have DEBUG=True, so this check is disabled.
+        with self.assertRaises(SuspiciousOperation):
-        request = HttpRequest()
+            request = HttpRequest()
-        request.META = {
+            request.META = {'HTTP_HOST': 'example.com'}
-            'HTTP_HOST': "invalid_hostname.com",
+            request.get_host()
-        }
-        self.assertEqual(request.get_host(), "invalid_hostname.com")
 
     @override_settings(ALLOWED_HOSTS=[])
     def test_get_host_suggestion_of_allowed_host(self):