CVE-2021-39164

Impact

### 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 security@matrix.org.

Affected packages

Affected products

Weakness classification

References

• NVD record
• CVE.org record
• GitHub advisory
• https://github.com/matrix-org/synapse/commit/cb35df940a
• https://github.com/matrix-org/synapse/releases/tag/v1.41.1
• https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q
• 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/advisories/GHSA-3x4c-pq33-4w3q
• https://nvd.nist.gov/vuln/detail/CVE-2021-39164
• https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-425.yaml
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN