---
id: CVE-2018-16515
aliases:
  - GHSA-fmvh-rvq5-hhjx
  - PYSEC-2026-845
title: Matrix Synapse Improper Signature Validation
summary: Matrix Synapse Improper Signature Validation
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - 'matrix-synapse >= 0.33.3, < 0.33.3.1'
  - matrix-synapse < 0.33.2.1
patched:
  - matrix-synapse 0.33.3.1
  - matrix-synapse 0.33.2.1
published: '2022-05-13'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-fmvh-rvq5-hhjx'
references:
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2018-16515'
  - url: 'https://github.com/matrix-org/synapse/issues/3796#event-1833126269'
  - url: >-
      https://github.com/matrix-org/synapse/commit/5bf8bc79ebc22c61968f2eb487714813fccbdb9b
  - url: >-
      https://github.com/matrix-org/synapse/commit/804dd41e18c449e711e443398b95c9f6c68b6fa2
  - url: >-
      https://github.com/matrix-org/synapse/commit/a5a0bf5cf71caed3c4e3677d2bce667c147dadfc
  - url: >-
      https://github.com/matrix-org/synapse/commit/c127c8d0421f0228a46ebbe280c9537e8d8ea42b
  - url: 'https://github.com/matrix-org/synapse'
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/IRW7YR2H3ASUSYX4AO4KMY3FNVDNYW3P
  - url: >-
      https://matrix.org/blog/2018/09/06/critical-security-update-synapse-0-33-3-1
tags:
  - osv
  - pip
epss: 0.01538
epssPercentile: 0.73766
ingestedAt: '2026-07-08T18:25:48.949Z'
---

## Overview

Matrix Synapse before 0.33.3.1 and 0.33.2.1 allows remote attackers to spoof events and possibly have unspecified other impacts by leveraging improper transaction and event signature validation.

## Affected packages

- `matrix-synapse >= 0.33.3, < 0.33.3.1`
- `matrix-synapse < 0.33.2.1`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 0.33.3.1`
- `matrix-synapse 0.33.2.1`