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Fencer Vulns
low 3.1

CVE-2021-39164 json

Improper authorisation of /members discloses room membership to non-members

published 2021-08-31 5 y ago modified 2026-07-08 4 mo ago also GHSA-3x4c-pq33-4w3q , PYSEC-2021-425 , EUVD-2021-0132

cvss
3.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.5%
EPSS 1.5% chance of exploitation in 30 days, percentile 73%
public exploits
0
none known

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.

Patch / fix

  • pypi matrix-synapse 1.41.1
  • matrix synapse 1.41.1
  • matrix-synapse openSUSE Tumbleweed 1.43.0-1.1

opensuse advisories openSUSE-SU-2024:11041-1

  • synapse Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 1.41.1-r0

alpine advisories ALPINE-CVE-2021-39164

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • matrix-synapse Arch Linux 1.41.1-1

arch linux advisories AVG-2334

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-39164 updated cvss 3.1

matrix-synapse: Improper authorisation of /members discloses room membership to non-members

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.45% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 2.0 3.5 AV:N/AC:M/Au:S/C:P/I:N/A:N
GitHub 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

Affected packages

ecosystem package affected fixed in
pypi matrix-synapse
<1.41.1
1.41.1

Affected products

  • matrix-org synapse

Classification

Weakness
  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
  • CWE-863 Incorrect Authorization

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.