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Vulnerability · Published Aug 31, 2021 · Assigned by GitHub_M

CVE-2021-39163Adding a private/unlisted room to a community exposes room metadata in an unauthorised manner.

Low 3.1

In plain English

A low-severity information exposure in synapse from matrix-org. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.9% (higher than 60% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.1Low
Exploit odds (30 days)0.9%top 40.3% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known

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 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`.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.20synapse1.41.1-r0ALPINE-CVE-2021-39163
Alpine:v3.21synapse1.41.1-r0ALPINE-CVE-2021-39163
Alpine:v3.22synapse1.41.1-r0ALPINE-CVE-2021-39163
Alpine:v3.23synapse1.41.1-r0ALPINE-CVE-2021-39163
Alpine:v3.24synapse1.41.1-r0ALPINE-CVE-2021-39163
Debian:14matrix-synapse1.41.1-1DEBIAN-CVE-2021-39163
PyPImatrix-synapse1.41.1GHSA-jj53-8fmw-f2w2
PyPImatrix-synapse1.41.1PYSEC-2021-424

Affected products (as reported)

VendorProductVersions
matrix-org synapse < 1.41.1

Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

References