CVE-2021-41281 Explained : Impact and Mitigation

Synapse instances with the media repository enabled are vulnerable to path traversal prior to version 1.47.1, allowing arbitrary file downloads. Upgrade to version 1.47.1 or later to mitigate.

Understanding CVE-2021-41281

Synapse is a package for Matrix homeservers written in Python 3/Twisted. The vulnerability allows unauthorized file downloads in specific server configurations.

What is CVE-2021-41281?

Prior to version 1.47.1, Synapse instances with media repository enabled can be tricked into downloading a file from a remote server into an arbitrary directory without authentication.

The Impact of CVE-2021-41281

The vulnerability has a CVSS base score of 7.5 (High severity) indicating a significant risk due to the potential for attackers to compromise file integrity.

Technical Details of CVE-2021-41281

The following provides more technical insights into the vulnerability.

Vulnerability Description

Synapse instances with media repository enabled can be tricked into path traversal, allowing unauthorized downloads into arbitrary directories.

Affected Systems and Versions

Product: Synapse
Vendor: Matrix-org
Versions affected: < 1.47.1

Exploitation Mechanism

The vulnerability stems from improper restriction of pathname, permitting path traversal attacks.

Mitigation and Prevention

Follow these steps to mitigate the CVE-2021-41281 vulnerability.

Immediate Steps to Take

Upgrade Synapse to version 1.47.1 or later.
Consider blocking certain endpoints as a temporary workaround if using a reverse proxy.

Long-Term Security Practices

Enable a federation whitelist to restrict access.
Regularly update and patch Synapse to address security vulnerabilities.
Configure non-containerized deployments with hardened systemd config.