CVE-2021-21394 : Exploit Details and Defense Strategies
Learn about CVE-2021-21394, a vulnerability in Synapse homeserver that leads to resource exhaustion due to missing input validation. Find out the impact, affected systems, and mitigation steps.
Synapse is a Matrix reference homeserver that suffers from a denial of service vulnerability due to missing input validation on third-party identifier endpoints. This could lead to resource exhaustion by causing excessive use of disk space and memory.
Understanding CVE-2021-21394
This CVE refers to a vulnerability within the Synapse homeserver that could be exploited to carry out denial of service attacks.
What is CVE-2021-21394?
Synapse, a Matrix reference homeserver, lacks input validation on certain parameters of the endpoints used to confirm third-party identifiers, potentially resulting in resource exhaustion.
The Impact of CVE-2021-21394
The vulnerability could be leveraged by malicious actors to exhaust system resources, leading to denial of service conditions. The affected version is Synapse versions prior to 1.28.0.
Technical Details of CVE-2021-21394
The vulnerability is classified with a base score of 5.3, indicating a medium severity level. The impact includes high availability impact, with high attack complexity and privilege requirements.
Vulnerability Description
The issue arises from the lack of input validation in the process of confirming third-party identifiers, potentially resulting in resource exhaustion due to excessive disk space and memory consumption.
Affected Systems and Versions
Synapse versions before 1.28.0 are vulnerable to this denial of service issue due to improper input validation.
Exploitation Mechanism
Attackers can exploit this vulnerability by sending specially crafted requests to the endpoints responsible for confirming third-party identifiers, causing resource exhaustion.
Mitigation and Prevention
To mitigate the risks associated with CVE-2021-21394, immediate steps should be taken by system administrators to secure their systems and prevent exploitation.
Immediate Steps to Take
Administrators are advised to update their Synapse installations to version 1.28.0 or newer to address the input validation issue and prevent resource exhaustion.
Long-Term Security Practices
Implementing secure coding practices, performing regular security audits, and staying informed about security updates are essential for long-term system security.
Patching and Updates
Regularly applying patches and updates released by the vendor, Matrix-org, is crucial to maintain a secure and resilient system.