---
id: CVE-2025-61672
aliases:
  - GHSA-fh66-fcv5-jjfr
  - PYSEC-2026-1612
title: Synapse's invalid device keys degrade federation functionality
summary: Synapse's invalid device keys degrade federation functionality
severity: medium
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - matrix-synapse < 1.138.3
  - 'matrix-synapse >= 1.139.0rc2, < 1.139.1'
patched:
  - matrix-synapse 1.138.3
  - matrix-synapse 1.139.1
published: '2025-10-08'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-fh66-fcv5-jjfr'
references:
  - url: >-
      https://github.com/element-hq/synapse/security/advisories/GHSA-fh66-fcv5-jjfr
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-61672'
  - url: 'https://github.com/element-hq/synapse/pull/17097'
  - url: >-
      https://github.com/element-hq/synapse/commit/26aaaf9e48fff80cf67a20c691c75d670034b3c1
  - url: >-
      https://github.com/element-hq/synapse/commit/7069636c2d6d1ef2022287addf3ed8b919ef2740
  - url: 'https://github.com/element-hq/synapse'
  - url: 'https://github.com/element-hq/synapse/releases/tag/v1.138.3'
  - url: 'https://github.com/element-hq/synapse/releases/tag/v1.138.4'
  - url: 'https://github.com/element-hq/synapse/releases/tag/v1.139.1'
  - url: 'https://github.com/element-hq/synapse/releases/tag/v1.139.2'
tags:
  - osv
  - pip
epss: 0.00466
epssPercentile: 0.39534
ingestedAt: '2026-07-08T18:25:48.912Z'
---

## Overview

### Impact

Lack of validation for device keys in Synapse before 1.138.3 and in Synapse 1.139.0 allow an attacker registered on the victim homeserver to degrade federation functionality, unpredictably breaking outbound federation to other homeservers. 

### Patches

Patched in Synapse 1.138.3, 1.138.4, 1.139.1, and 1.139.2.

Note that even though 1.138.3 and 1.139.1 fix the vulnerability, they inadvertently introduced an unrelated regression. For this reason, it is recommend to skip these releases and upgrading straight to 1.138.4 and 1.139.2.

### Workarounds

The vulnerability can only be exploited by users registered on the victim homeserver.

## Affected packages

- `matrix-synapse < 1.138.3`
- `matrix-synapse >= 1.139.0rc2, < 1.139.1`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 1.138.3`
- `matrix-synapse 1.139.1`