Check if instances are lists, not sequences. (#12128)

As a str is a sequence, the checks were not granular
enough and would allow lists or strings, when only
lists were valid.

1 files changed, 1 insertions, 1 deletions

diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py

index 55c2cbdba8..3979cbba71 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -857,7 +857,7 @@ class _RoomEntry:
 
 def _has_valid_via(e: EventBase) -> bool:
     via = e.content.get("via")
-    if not via or not isinstance(via, Sequence):
+    if not via or not isinstance(via, list):
         return False
     for v in via:
         if not isinstance(v, str):