GHSA-3x4c-pq33-4w3q Improper authorisation of members discloses room membership to non-members

• PyPI matrix-synapse: < 1.41.1 → fixed in 1.41.1

Impact 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. Patches Server administrators should upgrade to 1.41.1 or later. Workarounds 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 References n/a For more information If you have any questions or comments about this advisory, e-mail us at [email protected].