{"cve":"CVE-2021-39164","nvd":{"published":"2021-08-31T17:15:08.267","modified":"2026-06-17T04:03:13.710","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N","score":3.1},"cwes":["CWE-863","CWE-200"],"references":["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/"],"products":["fedoraproject:fedora","matrix:synapse"],"source":"nvd","synced_at":"2026-10-19T21:21:57.125947417+00:00"},"epss":{"cve":"CVE-2021-39164","score":0.01451,"percentile":0.7338,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-3x4c-pq33-4w3q","url":"https://osv.dev/vulnerability/GHSA-3x4c-pq33-4w3q","summary":"Improper authorisation of members discloses room membership to non-members","modified":"2026-07-08T06:28:52.954705259Z","packages":[{"ecosystem":"PyPI","name":"matrix-synapse","purl":"pkg:pypi/matrix-synapse","ranges":["<1.41.1"],"fixed":["1.41.1"]}]},{"id":"PYSEC-2021-425","url":"https://osv.dev/vulnerability/PYSEC-2021-425","summary":"","modified":"2026-02-26T23:26:01.587712Z","packages":[{"ecosystem":"PyPI","name":"matrix-synapse","purl":"pkg:pypi/matrix-synapse","ranges":["<1.41.1"],"fixed":["1.41.1"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}