Make sure a retention policy is a state event (#8527)

* Make sure a retention policy is a state event

* Changelog

1 files changed, 3 insertions, 0 deletions

diff --git a/synapse/events/validator.py b/synapse/events/validator.py

index 9df35b54ba..5f9af8529b 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -83,6 +83,9 @@ class EventValidator:
         Args:
             event (FrozenEvent): The event to validate.
         """
+        if not event.is_state():
+            raise SynapseError(code=400, msg="must be a state event")
+
         min_lifetime = event.content.get("min_lifetime")
         max_lifetime = event.content.get("max_lifetime")