CVE-2021-39164

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.

How to fix CVE-2021-39164

To remediate CVE-2021-39164, upgrade the affected package to a fixed version below.

—upgrade to 1.41.1-1 or later
—upgrade to 1.41.1 or later
—upgrade to cb35df940a828bc40b96daed997b5ad4c7842fd3 or later

Is CVE-2021-39164 being exploited?

Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

from 0, < 1.41.1-1
from 0, < 1.41.1
from 0, < cb35df940a828bc40b96daed997b5ad4c7842fd3 | from 0, < 1.41.1

CVSS scores

Source	Version	Severity	Vector
osv	CVSS 3.1	LOW3.1	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N