CVE-2021-39163Low· 3.1▾ SunlitAdding a private/unlisted room to a community exposes room metadata in an unauthorised manner.
▾ Sunlit zone — Low / medium · no exploitation signal
impact 17.1 · likelihood 0.2 · exploitation 0
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Exploit-prediction probability, daily snapshots since Jul 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via OSV
Last analysed / modified upstream
0.9%
0.9% → 0.9%
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:
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.
Server administrators should upgrade to 1.41.1 or higher.
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}/roomsn/a
If you have any questions or comments about this advisory, e-mail us at [email protected].
matrix-synapse < 1.41.1Upgrade to a patched release:
matrix-synapse 1.41.1Connected by shared product, vendor, weakness, or advisory.
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