GHSA-x345-32rc-8h85

Denial of service attack via push rule patterns in matrix-synapse

Source: GitHub Advisory Database (reviewed) Moderate CVE-2021-29471

Packages

Ecosystem	Package	Affected	Fixed in
PyPI	matrix-synapse	< 1.33.2	1.33.2

Details

As written in the advisory (Markdown source, shown as plain text).

### Impact "Push rules" can specify [conditions](https://matrix.org/docs/spec/client_server/r0.6.1#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. ### Patches The issue is patched by https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c. ### Workarounds A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy. ### For more information If you have any questions or comments about this advisory, email us at [email protected].

References

External links from the advisory. They lead to third-party sites.