CVE-2021-21332: Fedoraproject Fedora

High severity, CVSS 8.2. EPSS: 1.2% chance of exploitation in the next 30 days.

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.

Affected products

• Fedoraproject Fedora: version 34 only
• Matrix Synapse: before 1.27.0 (fixed in 1.27.0)

Published 2021-03-26. Last modified 2026-06-17.