From cf89266b980b62a6d8547f8e1ae9394359a05fc8 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 31 Jul 2019 16:03:14 +0100
Subject: [PATCH 1/2] Deny redaction of events in a different room.

We already correctly filter out such redactions, but we should also deny
them over the CS API.
---
 synapse/handlers/message.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index e951c39fa7e9..a5e23c4caf90 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -795,7 +795,6 @@ def is_inviter_member_event(e):
                 get_prev_content=False,
                 allow_rejected=False,
                 allow_none=True,
-                check_room_id=event.room_id,
             )
 
             # we can make some additional checks now if we have the original event.
@@ -803,6 +802,9 @@ def is_inviter_member_event(e):
                 if original_event.type == EventTypes.Create:
                     raise AuthError(403, "Redacting create events is not permitted")
 
+                if original_event.room_id != event.room_id:
+                    raise SynapseError(400, "Cannot redact event from a different room")
+
             prev_state_ids = yield context.get_prev_state_ids(self.store)
             auth_events_ids = yield self.auth.compute_auth_events(
                 event, prev_state_ids, for_verification=True

From 0eefb76fa1a4348a50843097a92ead108cec398c Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 31 Jul 2019 16:13:57 +0100
Subject: [PATCH 2/2] Newsfile

---
 changelog.d/5802.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/5802.misc

diff --git a/changelog.d/5802.misc b/changelog.d/5802.misc
new file mode 100644
index 000000000000..de31192652da
--- /dev/null
+++ b/changelog.d/5802.misc
@@ -0,0 +1 @@
+Deny redactions of events sent in a different room.