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Improper authorisation of members discloses room membership to non-members

Low severity GitHub Reviewed Published Aug 31, 2021 in matrix-org/synapse • Updated Sep 24, 2024

Package

pip matrix-synapse (pip)

Affected versions

< 1.41.1

Patched versions

1.41.1

Description

Impact

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.

Patches

Server administrators should upgrade to 1.41.1 or later.

Workarounds

Administrators of servers that use a reverse proxy could, with potentially unacceptable loss of functionality, block the following endpoints:

  • /_matrix/client/r0/rooms/{room_id}/members with at query parameter
  • /_matrix/client/unstable/rooms/{room_id}/members with at query parameter

References

n/a

For more information

If you have any questions or comments about this advisory, e-mail us at [email protected].

References

@richvdh richvdh published to matrix-org/synapse Aug 31, 2021
Published by the National Vulnerability Database Aug 31, 2021
Reviewed Aug 31, 2021
Published to the GitHub Advisory Database Sep 1, 2021
Last updated Sep 24, 2024

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS score

0.083%
(37th percentile)

Weaknesses

CVE ID

CVE-2021-39164

GHSA ID

GHSA-3x4c-pq33-4w3q

Source code

Credits

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