HOMEVULNERABILITIESCVE-2021-39164
LOW

CVE-2021-39164

CWE-200Published: August 31, 2021· Updated: Jun 17, 2026

3.1
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-39164 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

From a weakness classification perspective (CWE-200): Information exposure vulnerabilities leak sensitive data to unauthorized actors.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityHigh
Privileges Req.Low
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityLow
IntegrityNone
AvailabilityNone
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

Affected Vendors & Products

Fedora1 product(s)
fedora
matrix1 product(s)
synapse
Source: NVD CPE · 3 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://github.com/matrix-org/synapse/commit/cb35df940a
PATCHhttps://github.com/matrix-org/synapse/commit/cb35df940a
ADVISORYhttps://github.com/matrix-org/synapse/releases/tag/v1.41.1
ADVISORYhttps://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q
ADVISORYhttps://github.com/matrix-org/synapse/releases/tag/v1.41.1
ADVISORYhttps://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q

All References (10)

→
https://github.com/matrix-org/synapse/commit/cb35df940aPatch · Third Party Advisory
→
https://github.com/matrix-org/synapse/releases/tag/v1.41.1Release Notes · Third Party Advisory
→
https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3qThird Party Advisory
→
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/commit/cb35df940aPatch · Third Party Advisory
→
https://github.com/matrix-org/synapse/releases/tag/v1.41.1Release Notes · Third Party Advisory
→
https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3qThird Party Advisory
→
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/

Quick Facts

CVE IDCVE-2021-39164
CVSS Score3.1 / 10
SeverityLOW
WeaknessCWE-200
CISA KEVNo
Affected2 vendor(s)
PublishedAug 31, 2021

Related CVEs (CWE-200)

CVE-2025-22612
10.0
CVE-2011-3497
10.0
CVE-2025-29270
10.0
CVE-2025-61481
10.0
CVE-2022-29165
10.0
CVE-2026-27604
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-39164 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
← All Vulnerabilities·Search for CVE-2021-39164·NVD