low
3.5
CWE
200 863
Advisory Published
Advisory Published
Updated

CVE-2021-39163: Adding a private/unlisted room to a community exposes room metadata in an unauthorised manner.

First published: Tue Aug 31 2021(Updated: )

### Impact Unauthorised users can access the name, avatar, topic and number of members of a room if they know the ID of the room. This vulnerability is limited to homeservers where: - the vulnerable homeserver is in the room; and - untrusted users are permitted to create groups (communities). By default, only homeserver administrators can create groups. However, homeserver administrators can already access this information in the database or using the admin API. As a result, only homeservers where the configuration setting `enable_group_creation` has been set to `true` are impacted. ### Patches Server administrators should upgrade to 1.41.1 or higher. ### Workarounds Server administrators can set `enable_group_creation` to `false` in their homeserver configuration (this is the default value) to prevent creation of groups by non-administrators. Administrators that are using a reverse proxy could, with partial loss of group functionality, block the following endpoints: * `/_matrix/client/r0/groups/{group_id}/rooms` * `/_matrix/client/unstable/groups/{group_id}/rooms` ### References n/a ### For more information If you have any questions or comments about this advisory, e-mail us at security@matrix.org.

Credit: security-advisories@github.com security-advisories@github.com

Affected SoftwareAffected VersionHow to fix
Matrix Synapse<1.41.1
Fedoraproject Fedora=34
Fedoraproject Fedora=35
pip/matrix-synapse<1.41.1
1.41.1

Remedy

https://github.com/matrix-org/synapse/commit/cb35df940a

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Reference Links

Frequently Asked Questions

  • What is CVE-2021-39163?

    CVE-2021-39163 is a vulnerability in Matrix Synapse, an ecosystem for open federated Instant Messaging and Voice over IP, where unauthorised users can access certain information of a room if they know the room ID.

  • What is the severity of CVE-2021-39163?

    The severity of CVE-2021-39163 is low, with a CVSS severity score of 3.1.

  • How can unauthorised users access room information in CVE-2021-39163?

    Unauthorised users can access the name, avatar, topic, and number of members of a room if they know the ID of the room.

  • Which software versions are affected by CVE-2021-39163?

    Versions 1.41.0 and prior of Matrix Synapse and Fedora 34 and Fedora 35 are affected by CVE-2021-39163.

  • How do I fix CVE-2021-39163?

    To fix CVE-2021-39163, upgrade to version 1.41.1 of Matrix Synapse.

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