add some rate limiting to the password reset functionality

common/djangoapps/student/tests/tests.py

@@ -11,6 +11,7 @@
 from datetime import datetime, timedelta
 import pytz
 
+from django.core.cache import cache
 from django.conf import settings
 from django.test import TestCase
 from django.test.utils import override_settings
@@ -89,6 +90,23 @@ def test_nonexist_email_password_reset(self):
             'value': "('registration/password_reset_done.html', [])",
         })
 
+    @patch('student.views.render_to_string', Mock(side_effect=mock_render_to_string, autospec=True))
+    def test_password_reset_ratelimited(self):
+        """ Try (and fail) resetting password 30 times in a row on an non-existant email address """
+        cache.clear()
+
+        for i in xrange(30):
+            good_req = self.request_factory.post('/password_reset/', {'email': 'thisdoesnotexist@foo.com'})
+            good_resp = password_reset(good_req)
+            self.assertEquals(good_resp.status_code, 200)
+
+        # then the rate limiter should kick in and give a HttpForbidden response
+        bad_req = self.request_factory.post('/password_reset/', {'email': 'thisdoesnotexist@foo.com'})
+        bad_resp = password_reset(bad_req)
+        self.assertEquals(bad_resp.status_code, 403)
+
+        cache.clear()
+
     @unittest.skipIf(
         settings.FEATURES.get('DISABLE_RESET_EMAIL_TEST', False),
         dedent("""

common/djangoapps/student/views.py

@@ -72,6 +72,7 @@
 from dogapi import dog_stats_api
 
 from util.json_request import JsonResponse
+from util.bad_request_rate_limiter import BadRequestRateLimiter
 
 from microsite_configuration.middleware import MicrositeConfiguration
 
@@ -86,7 +87,6 @@
 Article = namedtuple('Article', 'title url author image deck publication publish_date')
 ReverifyInfo = namedtuple('ReverifyInfo', 'course_id course_name course_number date status display')  # pylint: disable=C0103
 
-
 def csrf_token(context):
     """A csrf token that can be included in a form."""
     csrf_token = context.get('csrf_token', '')
@@ -1345,12 +1345,23 @@ def password_reset(request):
     if request.method != "POST":
         raise Http404
 
+    # Add some rate limiting here by re-using the RateLimitMixin as a helper class
+    limiter = BadRequestRateLimiter()
+    if limiter.is_rate_limit_exceeded(request):
+        AUDIT_LOG.warning("Rate limit exceeded in password_reset")
+        return HttpResponseForbidden()
+
     form = PasswordResetFormNoActive(request.POST)
     if form.is_valid():
         form.save(use_https=request.is_secure(),
                   from_email=settings.DEFAULT_FROM_EMAIL,
                   request=request,
                   domain_override=request.get_host())
+    else:
+        # bad user? tick the rate limiter counter
+        AUDIT_LOG.info("Bad password_reset user passed in.")
+        limiter.tick_bad_request_counter(request)
+
     return JsonResponse({
         'success': True,
         'value': render_to_string('registration/password_reset_done.html', {}),

common/djangoapps/util/bad_request_rate_limiter.py

@@ -0,0 +1,23 @@
+"""
+A utility class which wraps the RateLimitMixin 3rd party class to do bad request counting
+which can be used for rate limiting
+"""
+from ratelimitbackend.backends import RateLimitMixin
+
+class BadRequestRateLimiter(RateLimitMixin):
+    """
+    Use the 3rd party RateLimitMixin to help do rate limiting on the Password Reset flows
+    """
+
+    def is_rate_limit_exceeded(self, request):
+        """
+        Returns if the client has been rated limited
+        """
+        counts = self.get_counters(request)
+        return sum(counts.values()) >= self.requests
+
+    def tick_bad_request_counter(self, request):
+        """
+        Ticks any counters used to compute when rate limt has been reached
+        """
+        self.cache_incr(self.get_cache_key(request))