Incorrect signature verification in django-ses

@@ -1,21 +1,25 @@
 import base64
 import logging
+import re
 import warnings
 from builtins import bytes
-
-from django_ses.deprecation import RemovedInDjangoSES20Warning
-
+from urllib.error import URLError
 from urllib.parse import urlparse
 from urllib.request import urlopen
-from urllib.error import URLError
 
 from django.core.exceptions import ImproperlyConfigured
+
 from django_ses import settings
+from django_ses.deprecation import RemovedInDjangoSES20Warning
 
 logger = logging.getLogger(__name__)
 
 _CERT_CACHE = {}
 
+SES_REGEX_CERT_URL = re.compile(
+    "(?i)^https://sns\.[a-z0-9\-]+\.amazonaws\.com(\.cn)?/SimpleNotificationService\-[a-z0-9]+\.pem$"
+)
+
 
 def clear_cert_cache():
     """Clear the certificate cache.
@@ -183,6 +187,17 @@ def _get_cert_url(self):
         url_obj = urlparse(cert_url)
         for trusted_domain in settings.EVENT_CERT_DOMAINS:
             parts = trusted_domain.split(".")
+            if "amazonaws.com" in trusted_domain:
+                if not SES_REGEX_CERT_URL.match(cert_url):
+                    if len(parts) < 4:
+                        return None
+                    else:
+                        logger.warning('Possible security risk for: "%s"', cert_url)
+                        logger.warning(
+                            "It is strongly recommended to configure the full domain in EVENT_CERT_DOMAINS. "
+                            "See v3.5.0 release notes for more details."
+                        )
+
             if url_obj.netloc.split(".")[-len(parts) :] == parts:
                 return cert_url
 
@@ -196,26 +211,28 @@ def _get_bytes_to_sign(self):
 
         # Depending on the message type the fields to add to the message
         # differ so we handle that here.
-        msg_type = self._data.get('Type')
-        if msg_type == 'Notification':
+        msg_type = self._data.get("Type")
+        if msg_type == "Notification":
             fields_to_sign = [
-                'Message',
-                'MessageId',
-                'Subject',
-                'Timestamp',
-                'TopicArn',
-                'Type',
+                "Message",
+                "MessageId",
+                "Subject",
+                "Timestamp",
+                "TopicArn",
+                "Type",
             ]
-        elif (msg_type == 'SubscriptionConfirmation' or
-              msg_type == 'UnsubscribeConfirmation'):
+        elif (
+            msg_type == "SubscriptionConfirmation"
+            or msg_type == "UnsubscribeConfirmation"
+        ):
             fields_to_sign = [
-                'Message',
-                'MessageId',
-                'SubscribeURL',
-                'Timestamp',
-                'Token',
-                'TopicArn',
-                'Type',
+                "Message",
+                "MessageId",
+                "SubscribeURL",
+                "Timestamp",
+                "Token",
+                "TopicArn",
+                "Type",
             ]
         else:
             # Unrecognized type
@@ -237,14 +254,14 @@ def _get_bytes_to_sign(self):
 
 def BounceMessageVerifier(*args, **kwargs):
     warnings.warn(
-        'utils.BounceMessageVerifier is deprecated. It is renamed to EventMessageVerifier.',
+        "utils.BounceMessageVerifier is deprecated. It is renamed to EventMessageVerifier.",
         RemovedInDjangoSES20Warning,
     )
 
     # parameter name is renamed from bounce_dict to notification.
-    if 'bounce_dict' in kwargs:
-        kwargs['notification'] = kwargs['bounce_dict']
-        del kwargs['bounce_dict']
+    if "bounce_dict" in kwargs:
+        kwargs["notification"] = kwargs["bounce_dict"]
+        del kwargs["bounce_dict"]
 
     return EventMessageVerifier(*args, **kwargs)
 
@@ -262,31 +279,32 @@ def verify_bounce_message(msg):
     Verify an SES/SNS bounce(event) notification message.
     """
     warnings.warn(
-        'utils.verify_bounce_message is deprecated. It is renamed to verify_event_message.',
+        "utils.verify_bounce_message is deprecated. It is renamed to verify_event_message.",
         RemovedInDjangoSES20Warning,
     )
     return verify_event_message(msg)
 
 
 def confirm_sns_subscription(notification):
     logger.info(
-        'Received subscription confirmation: TopicArn: %s',
-        notification.get('TopicArn'),
+        "Received subscription confirmation: TopicArn: %s",
+        notification.get("TopicArn"),
         extra={
-            'notification': notification,
+            "notification": notification,
         },
     )
 
     # Get the subscribe url and hit the url to confirm the subscription.
-    subscribe_url = notification.get('SubscribeURL')
+    subscribe_url = notification.get("SubscribeURL")
     try:
         urlopen(subscribe_url).read()
     except URLError as e:
         # Some kind of error occurred when confirming the request.
         logger.error(
-            'Could not confirm subscription: "%s"', e,
+            'Could not confirm subscription: "%s"',
+            e,
             extra={
-                'notification': notification,
+                "notification": notification,
             },
             exc_info=True,
         )