Unauthorised users can access the membership (list of members, with their display names) of a room if they know the ID of the room. The vulnerability is limited to rooms with shared
history visibility. Furthermore, the unauthorised user must be using an account on a vulnerable homeserver that is in the room.
Server administrators should upgrade to 1.41.1 or later.
Administrators of servers that use a reverse proxy could, with potentially unacceptable loss of functionality, block the following endpoints:
* /_matrix/client/r0/rooms/{room_id}/members
with at
query parameter
* /_matrix/client/unstable/rooms/{room_id}/members
with at
query parameter
n/a
If you have any questions or comments about this advisory, e-mail us at security@matrix.org.