CVE-2021-39163 : Security Advisory and Response

CVE-2021-39163, titled "Adding a private/unlisted room to a community exposes room metadata in an unauthorised manner" involves an exploitation scenario within Matrix's ecosystem for open federated Instant Messaging and Voice over IP.

Understanding CVE-2021-39163

This section provides deeper insight into the vulnerability and its impact.

What is CVE-2021-39163?

The vulnerability allows unauthorized users in certain scenarios to access specific room information in the Matrix platform.

The Impact of CVE-2021-39163

The vulnerability has a low base severity score of 3.1 according to CVSS, allowing unauthorized exposure of sensitive information to unprivileged actors.

Technical Details of CVE-2021-39163

Explore the technical aspects of this CVE for a better understanding.

Vulnerability Description

In versions prior to 1.41.1, untrusted users can obtain room details if the vulnerable homeserver is part of the room and non-administrators are allowed to create groups.

Affected Systems and Versions

Product: synapse
Vendor: matrix-org
Versions Affected: < 1.41.1

Exploitation Mechanism

An unauthorized user knowing the room ID can access room details in scenarios where unprivileged users can create groups.

Mitigation and Prevention

Discover the steps to mitigate and prevent exploitation of CVE-2021-39163.

Immediate Steps to Take

Upgrade to version 1.41.1 or higher to patch the vulnerability.
Set

enable_group_creation

to

false

to prevent non-administrators from creating groups.
Consider blocking specific endpoints if using a reverse proxy.

Long-Term Security Practices

Regularly update the Matrix server software.
Conduct security assessments to identify and address vulnerabilities proactively.

Patching and Updates

Ensure timely installation of updates and patches to maintain the security of the Matrix server infrastructure.