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 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. Server administrators should upgrade to 1.41.1 or higher to patch the vulnerability. There are two potential 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 endpoints `/_matrix/client/r0/groups/{group_id}/rooms` and `/_matrix/client/unstable/groups/{group_id}/rooms`.
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
| Link | Tags |
|---|---|
| https://github.com/matrix-org/synapse/security/advisories/GHSA-jj53-8fmw-f2w2 | mitigation third party advisory |
| https://github.com/matrix-org/synapse/commit/cb35df940a | third party advisory patch |
| https://github.com/matrix-org/synapse/releases/tag/v1.41.1 | third party advisory release notes |
| https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN/ | vendor advisory |
| https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF/ | vendor advisory |