CVE-2021-29471

Description

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.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://security.archlinux.org/ASA-202105-19
• https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85
• https://nvd.nist.gov/vuln/detail/CVE-2021-29471
• https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c
• https://github.com/matrix-org/synapse
• https://github.com/matrix-org/synapse/releases/tag/v1.33.2
• https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-135.yaml
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY
• https://security-tracker.debian.org/tracker/CVE-2021-29471