CVE-2021-29471
LOW3.7EPSS 0.34%Denial of service attack via push rule patterns in matrix-synapse
Published: 5/13/2021Modified: 5/20/2026
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.
Affected packages (3)
- Debian/matrix-synapsefrom 0, < 1.33.2-1
- PyPI/matrix-synapsefrom 0, < 1.33.2
- PyPI/matrix-synapsefrom 0, < 03318a766cac9f8b053db2214d9c332a977d226c | from 0, < 1.33.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N |
| osv | CVSS 3.1 | LOW3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L |
References (8)
- ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2021-29471
- ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2021-29471
- PATCHhttps://github.com/matrix-org/synapse
- WEBhttps://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c
- WEBhttps://github.com/matrix-org/synapse/releases/tag/v1.33.2
- WEBhttps://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85
- WEBhttps://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-135.yaml
- WEBhttps://lists.fedoraproject.org/archives/list/[email protected]/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY