CVE-2021-29471

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.

• CWE-400
• CWE-331

• https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226cPatch, Third Party Advisory
• https://github.com/matrix-org/synapse/releases/tag/v1.33.2Release Notes, Third Party Advisory
• https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85Patch, Third Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
• https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226cPatch, Third Party Advisory
• https://github.com/matrix-org/synapse/releases/tag/v1.33.2Release Notes, Third Party Advisory
• https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85Patch, Third Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/

Published

May 11, 2021

Last Modified

Jun 17, 2026

Status

Modified

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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