CVE-2021-21274 : Exploit Details and Defense Strategies

This CVE-2021-21274 revolves around a vulnerability in Synapse, a Matrix reference homeserver, affecting versions prior to 1.25.0. A malicious homeserver could redirect requests to their .well-known file, resulting in a denial of service attack. Here's what you need to know about this security issue.

Understanding CVE-2021-21274

CVE-2021-21274 highlights a critical vulnerability in Synapse that allows a malicious homeserver to exploit the .well-known file, potentially causing a denial of service attack by consuming excess resources.

What is CVE-2021-21274?

Synapse, a Python-based Matrix homeserver, is susceptible to a form of denial of service attack through crafted requests to the .well-known file before version 1.25.0. This can severely impact server performance when interacting with untrusted servers.

The Impact of CVE-2021-21274

The impact of CVE-2021-21274 is rated as MEDIUM severity with a CVSS base score of 4.3. This vulnerability can be exploited over a network without requiring privileges and necessitates user interaction, leading to increased resource consumption.

Technical Details of CVE-2021-21274

Let's delve into the technical aspects to understand this vulnerability better.

Vulnerability Description

The vulnerability in Synapse allows a malicious homeserver to manipulate requests to the .well-known file, potentially causing significant resource consumption on the affected server.

Affected Systems and Versions

Synapse versions prior to 1.25.0 are impacted by this vulnerability, exposing any server that accepts federation requests from untrusted sources to the risk of a denial of service attack.

Exploitation Mechanism

By redirecting requests to the .well-known file, a malicious homeserver can trigger a denial of service attack, consuming excessive resources and affecting the performance of the target server.

Mitigation and Prevention

Understanding how to mitigate and prevent such vulnerabilities is crucial for maintaining a secure environment.

Immediate Steps to Take

Upgrade Synapse to version 1.25.0 or newer to mitigate the CVE-2021-21274 vulnerability. Additionally, consider applying restrictions using the

federation_domain_whitelist

setting to limit communication with trusted homeservers.

Long-Term Security Practices

Implement strict federation policies to minimize exposure to untrusted servers and regularly review and update security configurations to address potential threats effectively.

Patching and Updates

Stay informed about security updates from the vendor and promptly apply patches to address known vulnerabilities and enhance the overall security posture of the server.