CVE-2021-39164 — Improper authorisation of /members discloses room membership to non-members
Matrix is an ecosystem for open federated Instant Messaging and Voice over IP. In versions 1.41.0 and prior, unauthorised users can access the membership (list of members, with …
Published: 2021-08-31 · CVSS: 3.1 · CVSS 3.1
Matrix is an ecosystem for open federated Instant Messaging and Voice over IP. In versions 1.41.0 and prior, 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 in order to receive the patch. One workaround is available. Administrators of servers that use a reverse proxy could, with potentially unacceptable loss of functionality, block the endpoints: `/_matrix/client/r0/rooms/{room_id}/members` with `at` query parameter, and `/_matrix/client/unstable/rooms/{room_id}/members` with `at` query parameter.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7