---
id: CVE-2018-10657
aliases:
  - GHSA-vmcc-4p4x-x7wg
  - PYSEC-2026-846
title: Matrix Synapse DoS
summary: Matrix Synapse DoS
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - matrix-synapse < 0.28.1
patched:
  - matrix-synapse 0.28.1
published: '2022-05-14'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-vmcc-4p4x-x7wg'
references:
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2018-10657'
  - url: >-
      https://github.com/matrix-org/synapse/commit/33f469ba19586bbafa0cf2c7d7c35463bdab87eb
  - url: >-
      https://docs.google.com/document/d/1I3fi2S-XnpO45qrpCsowZv8P8dHcNZ4fsBsbOW7KABI/edit#heading=h.fj95ykuss7s1
  - url: 'https://github.com/matrix-org/synapse'
  - url: 'https://matrix.org/blog/2018/05/01/security-update-synapse-0-28-1'
tags:
  - osv
  - pip
  - in-the-wild
epss: 0.01454
epssPercentile: 0.71889
exploited: true
zeroDay: true
ingestedAt: '2026-07-08T18:25:53.343Z'
---

## Overview

Matrix Synapse before 0.28.1 is prone to a denial of service flaw where malicious events injected with depth = 2<sup>63</sup> - 1 render rooms unusable, related to `federation/federation_base.py` and `handlers/message.py`, as exploited in the wild in April 2018.

## Affected packages

- `matrix-synapse < 0.28.1`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 0.28.1`