{"id":"CVE-2021-29471","aliases":["GHSA-x345-32rc-8h85","PYSEC-2021-135"],"url":"https://o3.security/vulnerability/CVE-2021-29471","summary":"Denial of service attack via push rule patterns in matrix-synapse","details":"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.","published":"2021-05-11T15:15:08.507Z","modified":"2026-07-08T06:27:13.881281978Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"matrix-synapse","fixedVersion":"1.33.2"}],"fix":{"url":"https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c","label":"matrix-org/synapse@03318a7"},"references":[{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/"},{"type":"ADVISORY","url":"https://github.com/matrix-org/synapse/releases/tag/v1.33.2"},{"type":"FIX","url":"https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c"},{"type":"FIX","url":"https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-08T06:27:13.881281978Z"}}