Security advisory
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2021-39164
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 11:53 UTC · Revision 1
Source evidence
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.
osv:CVE-2021-39164
Complete source record
{
"id": "34a8c37aa4f28f4d27437516027d2d220e6cf3f1535056dd0eb53c44f5b6eaef",
"url": "https://osv.dev/vulnerability/CVE-2021-39164",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "CVE-2021-39164",
"summary": "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.",
"evidence": "osv:CVE-2021-39164",
"products": [],
"severity": "low",
"structured": {
"id": "CVE-2021-39164",
"aliases": [
"CVE-2021-39164",
"GHSA-3x4c-pq33-4w3q",
"PYSEC-2021-425"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/matrix-org/synapse",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "a4c8a2f08b735266fbbe2f259e640f00dc5e3a00"
},
{
"fixed": "cb35df940a"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "0"
},
{
"fixed": "1.41.1"
}
],
"source": "CPE_RANGE"
},
{
"range": [
{
"fixed": "cb35df940a"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "a4c8a2f08b735266fbbe2f259e640f00dc5e3a00"
}
],
"source": "REFERENCES_TAG",
"original_tag": "v1.41.1"
}
]
}
}
],
"versions": [
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"v1.41.0rc1",
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"v1.36.0rc1",
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"hhs-8",
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"v0.23.0-rc2",
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"v0.18.1",
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"v0.16.0",
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"v0.13.3",
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"v0.11.0-r1",
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"v0.9.0",
"v0.8.1-r4",
"v0.8.1-r3",
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"v0.8.1-r1",
"v0.8.1",
"v0.8.0",
"v0.7.1-r4",
"v0.7.1-r3",
"v0.7.1-r2",
"v0.7.1-r1",
"v0.7.1",
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"v0.7.0a",
"v0.7.0",
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"v0.6.1",
"v0.6.0b",
"v0.6.0a",
"v0.6.0",
"v0.5.4a",
"v0.5.4",
"v0.5.3c",
"v0.5.3b",
"v0.5.3a",
"v0.5.3",
"v0.5.2",
"v0.5.1",
"v0.5.0",
"v0.4.2",
"v0.4.1",
"v0.3.4",
"v0.3.3",
"v0.3.0",
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-39164.json"
}
}
],
"modified": "2026-10-20T10:54:53.368026967Z",
"provider": "osv",
"references": [
"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/releases/tag/v1.41.1",
"https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q",
"https://github.com/matrix-org/synapse/commit/cb35df940a"
],
"provider_metadata": {
"unresolved_ranges": [
{
"cpes": [
"cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*",
"cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*"
],
"vendor_product": "fedoraproject:fedora",
"extracted_events": [
{
"range": [
{
"introduced": "34"
},
{
"last_affected": "34"
},
{
"introduced": "35"
},
{
"last_affected": "35"
}
],
"source": "CPE_STRING"
}
]
}
]
}
},
"related_cves": [
{
"value": "CVE-2021-39164",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 386374,
"published_at": "2021-08-31T17:15:08.267+00:00"
}