CVE-2021-39164

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.

• CWE-200
• CWE-863

• https://github.com/matrix-org/synapse/commit/cb35df940aPatch, Third Party Advisory
• https://github.com/matrix-org/synapse/releases/tag/v1.41.1Release Notes, Third Party Advisory
• https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3qThird Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN/
• https://github.com/matrix-org/synapse/commit/cb35df940aPatch, Third Party Advisory
• https://github.com/matrix-org/synapse/releases/tag/v1.41.1Release Notes, Third Party Advisory
• https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3qThird Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN/

Published

Aug 31, 2021

Last Modified

Jun 17, 2026

Status

Modified