---
id: CVE-2023-45129
aliases:
  - GHSA-5chr-wjw5-3gq4
  - PYSEC-2023-199
title: >-
  matrix-synapse vulnerable to denial of service due to malicious server ACL
  events
summary: >-
  matrix-synapse vulnerable to denial of service due to malicious server ACL
  events
severity: medium
cvss: 4.9
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H'
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - matrix-synapse < 1.94.0
patched:
  - matrix-synapse 1.94.0
published: '2023-10-10'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:49:58.536596047Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-5chr-wjw5-3gq4'
references:
  - url: >-
      https://github.com/matrix-org/synapse/security/advisories/GHSA-5chr-wjw5-3gq4
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2023-45129'
  - url: 'https://github.com/matrix-org/synapse/pull/16360'
  - url: >-
      https://github.com/matrix-org/synapse/commit/f84da3c32ec74cf054e2fd6d10618aa4997cffaa
  - url: 'https://github.com/matrix-org/synapse'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-199.yaml
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/KEVRB4MG5UXQ5RLZHSUJXM5GWEBYYS5B
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/N6P4QULVUE254WI7XF2LWWOGHCYVFXFY
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WRO4MPQ6HOXIUZM6RJP6VTCTMV7RD2T3
  - url: >-
      https://matrix-org.github.io/synapse/latest/admin_api/rooms.html#version-2-new-version
  - url: 'https://security.gentoo.org/glsa/202401-12'
tags:
  - osv
  - pip
epss: 0.01166
epssPercentile: 0.65922
ingestedAt: '2026-09-12T03:13:01.659Z'
---

## Overview

### Impact
A malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service.

Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected.

### Patches
Server administrators are advised to upgrade to Synapse 1.94.0 or later.

### Workarounds
Rooms with malicious server ACL events can be [purged and blocked](https://matrix-org.github.io/synapse/latest/admin_api/rooms.html#version-2-new-version) using the admin API.


## Affected packages

- `matrix-synapse < 1.94.0`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 1.94.0`