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 parametern/a
If you have any questions or comments about this advisory, e-mail us at [email protected].
github.com/matrix-org/synapse
github.com/matrix-org/synapse/commit/cb35df940a
github.com/matrix-org/synapse/releases/tag/v1.41.1
github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q
lists.fedoraproject.org/archives/list/[email protected]/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF
lists.fedoraproject.org/archives/list/[email protected]/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN
nvd.nist.gov/vuln/detail/CVE-2021-39164