1 files changed, 8 insertions, 1 deletions
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index 0b530b9034..3b687957dd 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -199,7 +199,14 @@ class TypingHandler(object):
         user_id = content["user_id"]
 
         # Check that the string is a valid user id
-        UserID.from_string(user_id)
+        user = UserID.from_string(user_id)
+
+        if user.domain != origin:
+            logger.info(
+                "Got typing update from %r with bad 'user_id': %r",
+                origin, user_id,
+            )
+            return
 
         users = yield self.state.get_current_user_in_room(room_id)
         domains = set(get_domain_from_id(u) for u in users)