fix: thread will only be returned for matching course ID

lms/djangoapps/discussion/rest_api/api.py

@@ -1465,7 +1465,7 @@ def update_comment(request, comment_id, update_data):
     return api_comment
 
 
-def get_thread(request, thread_id, requested_fields=None):
+def get_thread(request, thread_id, requested_fields=None, course_id=None):
     """
     Retrieve a thread.
 
@@ -1476,6 +1476,8 @@ def get_thread(request, thread_id, requested_fields=None):
 
         thread_id: The id for the thread to retrieve
 
+        course_id: the id of the course the threads belongs to
+
         requested_fields: Indicates which additional fields to return for
         thread. (i.e. ['profile_image'])
     """
@@ -1489,6 +1491,8 @@ def get_thread(request, thread_id, requested_fields=None):
             "user_id": str(request.user.id),
         }
     )
+    if course_id and course_id != cc_thread.course_id:
+        raise ThreadNotFoundError("Thread not found.")
     return _serialize_discussion_entities(request, context, [cc_thread], requested_fields, DiscussionEntity.thread)[0]
 
 

lms/djangoapps/discussion/rest_api/tests/test_api.py

@@ -3993,6 +3993,14 @@ def test_group_access(self, role_name, course_is_cohorted, thread_group_state):
         except ThreadNotFoundError:
             assert expected_error
 
+    def test_course_id_mismatch(self):
+        """
+            Test if the api throws not found exception if course_id from params mismatches course_id in thread
+        """
+        self.register_thread()
+        get_thread(self.request, self.thread_id, 'different_course_id')
+        assert ThreadNotFoundError
+
 
 @mock.patch('lms.djangoapps.discussion.rest_api.api._get_course', mock.Mock())
 class CourseTopicsV2Test(ModuleStoreTestCase):

lms/djangoapps/discussion/rest_api/views.py

@@ -527,7 +527,8 @@ def retrieve(self, request, thread_id=None):
         Implements the GET method for thread ID
         """
         requested_fields = request.GET.get('requested_fields')
-        return Response(get_thread(request, thread_id, requested_fields))
+        course_id = request.GET.get('course_id')
+        return Response(get_thread(request, thread_id, requested_fields, course_id))
 
     def create(self, request):
         """