---
id: CVE-2024-31208
aliases:
  - GHSA-3h7q-rfh9-xm4v
  - PYSEC-2024-50
title: Synapse V2 state resolution weakness allows Denial of Service (DoS)
summary: Synapse V2 state resolution weakness allows Denial of Service (DoS)
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - matrix-synapse < 1.105.1
patched:
  - matrix-synapse 1.105.1
published: '2024-04-23'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:11.151283540Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-3h7q-rfh9-xm4v'
references:
  - url: >-
      https://github.com/element-hq/synapse/security/advisories/GHSA-3h7q-rfh9-xm4v
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2024-31208'
  - url: >-
      https://github.com/element-hq/synapse/commit/55b0aa847a61774b6a3acdc4b177a20dc019f01a
  - url: 'https://github.com/element-hq/synapse'
  - url: 'https://github.com/element-hq/synapse/releases/tag/v1.105.1'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2024-50.yaml
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/R6FCCO4ODTZ3FDS7TMW76PKOSEL2TQVB
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/RR53FNHV446CB37TP45GZ6F6HZLZCK3K
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VSF4NJJSTSQRJQ47PLYYSCFYKJBP7DET
tags:
  - osv
  - pip
epss: 0.01463
epssPercentile: 0.72483
ingestedAt: '2026-09-12T03:13:01.646Z'
---

## Overview

### Impact

A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in how the auth chain cover index is calculated. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service.

Servers in private federations, or those that do not federate, are not affected.

### Patches

Server administrators should upgrade to 1.105.1 or later.

### Workarounds

One can:
- ban the malicious users or ACL block servers from the rooms; and/or
- leave the room and purge the room using the admin API

### For more information

If you have any questions or comments about this advisory, please email us at [security AT element.io](mailto:security@element.io).

## Affected packages

- `matrix-synapse < 1.105.1`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 1.105.1`