CVE-2021-39164 Improper authorisation of /members discloses room membership to non-members

2021-08-3116:20:10

CWE-200

GitHub_M

www.cve.org

cve-2021-39164

improper authorisation

room membership disclosure

matrix ecosystem

unauthorised access

shared history visibility

vulnerable homeserver

server upgrade

reverse proxy blocking

CVSS3

3.1

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

LOW

Integrity Impact

NONE

Availability Impact

NONE

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

AI Score

Confidence

High

EPSS

0.001

Percentile

35.6%

JSON

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.

CNA Affected

[
  {
    "product": "synapse",
    "vendor": "matrix-org",
    "versions": [
      {
        "status": "affected",
        "version": "< 1.41.1"
      }
    ]
  }
]