CVE-2021-29471 Explained : Impact and Mitigation

This CVE-2021-29471 impacts the Matrix Synapse server, affecting versions prior to 1.33.2. The vulnerability allows for a denial-of-service attack when processing specific events due to poor performance in the event matching engine.

Understanding CVE-2021-29471

Matrix Synapse, a Python-based Matrix reference homeserver, contains a vulnerability that can lead to denial-of-service attacks when processing moderate length events.

What is CVE-2021-29471?

Synapse before version 1.33.2 allows 'Push rules' to match conditions based on event content, causing a denial-of-service vulnerability due to poor performance in the matching engine.

The Impact of CVE-2021-29471

The base CVSS score for this vulnerability is 3.7, with a low impact on availability and no impact on confidentiality or integrity.

Technical Details of CVE-2021-29471

This section covers the technical aspects of the CVE.

Vulnerability Description

The vulnerability arises from specific patterns in push rules causing a significant performance impact on the matching engine, leading to a denial of service.

Affected Systems and Versions

Matrix Synapse versions prior to 1.33.2 are affected by this vulnerability.

Exploitation Mechanism

Attackers can exploit this vulnerability by triggering the specific conditions in the event matching engine to cause denial of service.

Mitigation and Prevention

Learn how to address and prevent the CVE-2021-29471 vulnerability.

Immediate Steps to Take

Update Matrix Synapse to version 1.33.2 to mitigate the vulnerability. Consider blocking custom push rules to prevent exploitation.

Long-Term Security Practices

Continuously monitor security advisories and promptly apply patches for known vulnerabilities like CVE-2021-29471.

Patching and Updates

Ensure timely deployment of patches and updates provided by Matrix Synapse to protect your system from exploits.