Learn about CVE-2021-21393, a Denial of Service vulnerability in Synapse Matrix homeserver. Explore its impact, technical details, affected systems, and mitigation steps.
Denial of Service (DoS) vulnerability in Synapse's Matrix reference homeserver before version 1.28.0 could lead to resource exhaustion due to missing input validation. This could result in excessive disk space and memory usage, impacting the availability of the service.
Understanding CVE-2021-21393
This CVE highlights a vulnerability in Matrix's Synapse server that could be exploited to exhaust system resources, affecting service availability.
What is CVE-2021-21393?
CVE-2021-21393 pertains to a DoS vulnerability in Synapse, a Matrix reference homeserver. The issue arises from inadequate input validation on groups/communities endpoints, potentially leading to resource exhaustion.
The Impact of CVE-2021-21393
The impact of this vulnerability is rated as MEDIUM. An attacker could exploit this flaw to consume excess disk space and memory, causing service disruption and denial of service.
Technical Details of CVE-2021-21393
This section dives into the technical aspects of the vulnerability.
Vulnerability Description
The vulnerability arises from missing input validation on endpoints for confirming third-party identifiers. This oversight could be leveraged to exhaust system resources.
Affected Systems and Versions
Synapse servers running versions earlier than 1.28.0 are affected by this vulnerability.
Exploitation Mechanism
By manipulating parameters on the groups/communities endpoints, an attacker could trigger resource exhaustion, impacting the server's availability.
Mitigation and Prevention
To address and prevent the exploitation of CVE-2021-21393, follow these recommendations:
Immediate Steps to Take
Long-Term Security Practices
Patching and Updates
Stay informed about security advisories from Matrix.org and promptly apply patches and updates to stay protected.