CVE-2018-6596 (published 2018-02-03T21:29Z)

webhooks/base.py in Anymail (aka django-anymail) before 1.2.1 is prone to a timing attack vulnerability on the WEBHOOK_AUTHORIZATION secret, which allows remote attackers to post arbitrary e-mail tracking events.

Severity: MEDIUM
CVSS v2 base score: 6.4 (AV:N/AC:L/Au:N/C:P/I:P/A:N)
CVSS v3 base score: 9.1, CRITICAL (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)

Weakness information:
cwe_id: CWE-200
cwe_name: Exposure of Sensitive Information to an Unauthorized Actor
description: The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
extended_description: 
	   There are many different kinds of mistakes that introduce information exposures. The severity of the error can range widely, depending on the context in which the product operates, the type of sensitive information that is revealed, and the benefits it may provide to an attacker.  Some kinds of sensitive information include:
       
         private, personal information, such as personal messages, financial data, health records, geographic location, or contact details
         system status and environment, such as the operating system and installed packages
		 business secrets and intellectual property
		 network status and configuration
		 the product's own code or internal state
         metadata, e.g. logging of connections or message headers
		 indirect information, such as a discrepancy between two internal operations that can be observed by an outsider
       
	    Information might be sensitive to different parties, each of which may have their own expectations for whether the information should be protected.  These parties include:
               
                  the product's own users
                  people or organizations whose information is created or used by the product, even if they are not direct product users
		  the product's administrators, including the admins of the system(s) and/or networks on which the product operates
                  the developer
               
	    Information exposures can occur in different ways:
               
                  the code explicitly inserts sensitive information into resources or messages that are intentionally made accessible to unauthorized actors, but should not contain the information - i.e., the information should have been "scrubbed" or "sanitized"
                  a different weakness or mistake indirectly inserts the sensitive information into resources, such as a web script error revealing the full system path of the program.
                  the code manages resources that intentionally contain sensitive information, but the resources are unintentionally made accessible to unauthorized actors. In this case, the information exposure is resultant - i.e., a different weakness enabled the access to the information in the first place.
               
	    It is common practice to describe any loss of confidentiality as an "information exposure," but this can lead to overuse of CWE-200 in CWE mapping. From the CWE perspective, loss of confidentiality is a technical impact that can arise from dozens of different weaknesses, such as insecure file permissions or out-of-bounds read.  CWE-200 and its lower-level descendants are intended to cover the mistakes that occur in behaviors that explicitly manage, store, transfer, or cleanse sensitive information.
         
         

Fix information:
repo_url: https://github.com/anymail/django-anymail
commit_details: repo_url: https://github.com/anymail/django-anymail
author: medmunds
author_date: 2018-02-02 11:41:14-08:00
msg: Security: prevent timing attack on WEBHOOK_AUTHORIZATION secret

Anymail's webhook validation was vulnerable to a timing attack.
An attacker could have used this to recover your WEBHOOK_AUTHORIZATION
shared secret, potentially allowing them to post fabricated or malicious
email tracking events to your app.

There have not been any reports of attempted exploit in the wild. (The
vulnerability was discovered through code review.) Attempts would be
visible in http logs as a very large number of 400 responses on
Anymail's webhook urls, or in Python error monitoring as a very large
number of AnymailWebhookValidationFailure exceptions.

If you are using Anymail's webhooks, you should upgrade to this release.
In addition, you may want to rotate to a new WEBHOOK_AUTHORIZATION
secret ([docs](http://anymail.readthedocs.io/en/stable/tips/securing_webhooks/#use-a-shared-authorization-secret)),
particularly if your logs indicate attempted exploit.
repository: repo_url: https://github.com/anymail/django-anymail
repo_name: anymail/django-anymail
description: Django email backends and webhooks for Amazon SES, Brevo (Sendinblue), MailerSend, Mailgun, Mailjet, Postmark, Postal, Resend, SendGrid, SparkPost, Unisender Go and more
repo_language: Python
owner: anymail
file_changes: filename: base.py
change_type: ModificationType.MODIFY
diff: @@ -2,6 +2,7 @@ import warnings
 
 import six
 from django.http import HttpResponse
+from django.utils.crypto import constant_time_compare
 from django.utils.decorators import method_decorator
 from django.views.decorators.csrf import csrf_exempt
 from django.views.generic import View
@@ -40,8 +41,13 @@ class AnymailBasicAuthMixin(object):
     def validate_request(self, request):
         """If configured for webhook basic auth, validate request has correct auth."""
         if self.basic_auth:
-            basic_auth = get_request_basic_auth(request)
-            if basic_auth is None or basic_auth not in self.basic_auth:
+            request_auth = get_request_basic_auth(request)
+            # Use constant_time_compare to avoid timing attack on basic auth. (It's OK that any()
+            # can terminate early: we're not trying to protect how many auth strings are allowed,
+            # just the contents of each individual auth string.)
+            auth_ok = any(constant_time_compare(request_auth, allowed_auth)
+                          for allowed_auth in self.basic_auth)
+            if not auth_ok:
                 # noinspection PyUnresolvedReferences
                 raise AnymailWebhookValidationFailure(
                     "Missing or invalid basic auth in Anymail %s webhook" % self.esp_name)
@@ -77,8 +83,11 @@ class AnymailBaseWebhookView(AnymailBasicAuthMixin, View):
         *All* definitions of this method in the class chain (including mixins)
         will be called. There is no need to chain to the superclass.
         (See self.run_validators and collect_all_methods.)
+
+        Security note: use django.utils.crypto.constant_time_compare for string
+        comparisons, to avoid exposing your validation to a timing attack.
         """
-        # if request.POST['signature'] != expected_signature:
+        # if not constant_time_compare(request.POST['signature'], expected_signature):
         #     raise AnymailWebhookValidationFailure("...message...")
         # (else just do nothing)
         pass

programming_language: Python