Bug 1999846 (CVE-2021-39163) - CVE-2021-39163 matrix-synapse: Adding a private/unlisted room to a community exposes room metadata in an unauthorised manner
Summary: CVE-2021-39163 matrix-synapse: Adding a private/unlisted room to a community ...
Alias: CVE-2021-39163
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1999847
TreeView+ depends on / blocked
Reported: 2021-08-31 19:28 UTC by Pedro Sampaio
Modified: 2021-09-01 00:56 UTC (History)
3 users (show)

Fixed In Version:
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Last Closed: 2021-09-01 00:56:16 UTC

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Description Pedro Sampaio 2021-08-31 19:28:08 UTC
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`.


Comment 1 Pedro Sampaio 2021-08-31 19:28:28 UTC
Created matrix-synapse tracking bugs for this issue:

Affects: fedora-all [bug 1999847]

Comment 2 Product Security DevOps Team 2021-09-01 00:56:16 UTC
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.

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