Bug 1999844 (CVE-2021-39164) - CVE-2021-39164 matrix-synapse: Improper authorisation of /members discloses room membership to non-members
Summary: CVE-2021-39164 matrix-synapse: Improper authorisation of /members discloses r...
Alias: CVE-2021-39164
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1999845
TreeView+ depends on / blocked
Reported: 2021-08-31 19:27 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 00:56:13 UTC

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Description Pedro Sampaio 2021-08-31 19:27:57 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 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. Server administrators should upgrade to 1.41.1 or later in order to receive the patch. One workaround is available. Administrators of servers that use a reverse proxy could, with potentially unacceptable loss of functionality, block the endpoints: `/_matrix/client/r0/rooms/{room_id}/members` with `at` query parameter, and `/_matrix/client/unstable/rooms/{room_id}/members` with `at` query parameter.


Comment 1 Pedro Sampaio 2021-08-31 19:28:12 UTC
Created matrix-synapse tracking bugs for this issue:

Affects: fedora-all [bug 1999845]

Comment 2 Product Security DevOps Team 2021-09-01 00:56:13 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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