CVE-2021-29471: Fedoraproject Fedora

Medium severity, CVSS 5.3. EPSS: 1.6% 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 1.33.2 "Push rules" can specify conditions under which they will match, including `event_match`, which matches event content against a pattern including wildcards. Certain patterns can cause very poor performance in the matching engine, leading to a denial-of-service when processing moderate length events. The issue is patched in version 1.33.2. A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.

Affected products

• Fedoraproject Fedora: version 34 only
• Matrix Synapse: before 1.33.2 (fixed in 1.33.2)

Published 2021-05-11. Last modified 2026-06-17.