[4.2.x] Fixed CVE-2024-45231 -- Avoided server error on password reset when email sending fails.

On successful submission of a password reset request, an email is sent
to the accounts known to the system. If sending this email fails (due to
email backend misconfiguration, service provider outage, network issues,
etc.), an attacker might exploit this by detecting which password reset
requests succeed and which ones generate a 500 error response.

Thanks to Thibaut Spriet for the report, and to Mariusz Felisiak, Adam
Johnson, and Sarah Boyce for the reviews.

2 files changed, 26 insertions, 0 deletions

diff --git a/tests/auth_tests/test_forms.py b/tests/auth_tests/test_forms.py
index 81c56a428e..f068d347a9 100644
--- a/tests/auth_tests/test_forms.py
+++ b/tests/auth_tests/test_forms.py
@@ -1245,6 +1245,27 @@ class PasswordResetFormTest(TestDataMixin, TestCase):
             )
         )
 
+    @override_settings(EMAIL_BACKEND="mail.custombackend.FailingEmailBackend")
+    def test_save_send_email_exceptions_are_catched_and_logged(self):
+        (user, username, email) = self.create_dummy_user()
+        form = PasswordResetForm({"email": email})
+        self.assertTrue(form.is_valid())
+
+        with self.assertLogs("django.contrib.auth", level=0) as cm:
+            form.save()
+
+        self.assertEqual(len(mail.outbox), 0)
+        self.assertEqual(len(cm.output), 1)
+        errors = cm.output[0].split("\n")
+        pk = user.pk
+        self.assertEqual(
+            errors[0],
+            f"ERROR:django.contrib.auth:Failed to send password reset email to {pk}",
+        )
+        self.assertEqual(
+            errors[-1], "ValueError: FailingEmailBackend is doomed to fail."
+        )
+
     @override_settings(AUTH_USER_MODEL="auth_tests.CustomEmailField")
     def test_custom_email_field(self):
         email = "test@mail.com"
diff --git a/tests/mail/custombackend.py b/tests/mail/custombackend.py
index 14e7f077ba..c6c567b642 100644
--- a/tests/mail/custombackend.py
+++ b/tests/mail/custombackend.py
@@ -12,3 +12,8 @@ class EmailBackend(BaseEmailBackend):
         # Messages are stored in an instance variable for testing.
         self.test_outbox.extend(email_messages)
         return len(email_messages)
+
+
+class FailingEmailBackend(BaseEmailBackend):
+    def send_messages(self, email_messages):
+        raise ValueError("FailingEmailBackend is doomed to fail.")