CVE-2021-21333 : Security Advisory and Response

Synapse, a Matrix reference homeserver, is prone to HTML injection in notification emails related to missed messages or expiring accounts. This vulnerability affects versions prior to 1.27.0, allowing attackers to insert forged content into the email. Learn more about CVE-2021-21333 and its impact, technical details, and mitigation steps.

Understanding CVE-2021-21333

This section provides insights into the HTML injection vulnerability affecting Synapse servers.

What is CVE-2021-21333?

CVE-2021-21333 highlights a security issue in Synapse servers where notification emails for missed messages and account expiry are susceptible to HTML injection.

The Impact of CVE-2021-21333

The vulnerability in versions prior to 1.27.0 can lead to forged content being inserted into notification emails, compromising the integrity of the communication.

Technical Details of CVE-2021-21333

Explore the technical aspects, affected systems, and exploitation mechanism of CVE-2021-21333.

Vulnerability Description

Synapse versions below 1.27.0 are vulnerable to HTML injection in notification emails, posing a risk of unauthorized content insertion.

Affected Systems and Versions

The vulnerability impacts Synapse servers running versions older than 1.27.0.

Exploitation Mechanism

Attackers can exploit this issue by injecting malicious HTML code into notification emails for missed messages or account expiration.

Mitigation and Prevention

Discover the immediate steps and long-term security practices to mitigate the risks associated with CVE-2021-21333.

Immediate Steps to Take

Update Synapse to version 1.27.0 to eliminate the HTML injection vulnerability.

Long-Term Security Practices

Regularly monitor and update your Matrix homeserver to address potential security vulnerabilities promptly.

Patching and Updates

Stay informed about security advisories and apply patches released by Matrix-org to enhance the security of your Synapse server.