CVE-2021-39163

Published: 31 August 2021

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`.

Priority

Cvss 3 Severity Score

3.1

Score breakdown

Status

Package	Release	Status
matrix-synapse Launchpad, Ubuntu, Debian	bionic	Needed
	focal	Needed
	hirsute	Ignored (end of life)
	impish	Ignored (end of life)
	jammy	Needs triage
	kinetic	Ignored (end of life, was needs-triage)
	lunar	Not vulnerable (1.64.0-3)
	mantic	Not vulnerable (1.64.0-3)
	noble	Not vulnerable (1.64.0-3)
	trusty	Does not exist
	upstream	Released (1.41.1-1)
	xenial	Ignored (end of standard support)

Severity score breakdown

Parameter	Value
Base score	3.1
Attack vector	Network
Attack complexity	High
Privileges required	Low
User interaction	None
Scope	Unchanged
Confidentiality	Low
Integrity impact	None
Availability impact	None
Vector	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

References

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