CVE-2021-29471
Certain patterns can cause very poor performance in the matching engine, leading to a denial-of-service when processing moderate length events.
Does this matter?
Lower severity and a low EPSS score (1.65%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- EPSS
- 1.65% probability · 75th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-400, CWE-331
- Affected
- matrix/synapse · fedoraproject/fedora
- Source
- security-advisories@github.com
References
- 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/
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.