CVE-2021-39164 Improper authorisation of /members discloses room membership to non-members
Unauthorized users can view room member lists in shared-history rooms if they know the room ID and use a vulnerable homeserver account.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-39164?
CVE-2021-39164 is a low-severity missing authorization vulnerability in Fedoraproject Fedora, published on 31 Aug 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2021-39164?
3 open source packages ship an affected version, including matrix-synapse. It affects 2 products.
| Package | Affected | Fixed in |
|---|---|---|
matrix-synapse PyPI | All versions | 1.41.1 |
matrix-synapse PyPI | All versions | 1.41.1 |
matrix-synapse PyPI | All versions | 1.41.1 |
Products include Fedoraproject Fedora, Matrix Synapse.
How do I fix CVE-2021-39164?
Upgrade matrix-synapse to 1.41.1 or later.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2021-39164 being exploited?
There is no known exploitation of CVE-2021-39164 in the wild and no public exploit code.
Other vulnerabilities in Fedoraproject Fedora
Sources
Also known as GHSA-3x4c-pq33-4w3q, PYSEC-2021-425, UBUNTU-CVE-2021-39164.