Synapse is an open source Matrix homeserver implementation. 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. The issue is 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, the maintainers of Synapse recommend skipping these releases and upgrading straight to 1.138.4 and 1.139.2.

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact Low

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Key SSVC decision points have not yet been added.

Affected Vendors & Products

Vendors Products
Element-hq
  • Synapse

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No data.

References
Link Providers
https://github.com/element-hq/synapse/commit/26aaaf9e48fff80cf67a20c691c75d670034b3c1 cve-icon cve-icon
https://github.com/element-hq/synapse/commit/7069636c2d6d1ef2022287addf3ed8b919ef2740 cve-icon cve-icon
https://github.com/element-hq/synapse/pull/17097 cve-icon cve-icon
https://github.com/element-hq/synapse/releases/tag/v1.138.3 cve-icon cve-icon
https://github.com/element-hq/synapse/releases/tag/v1.139.1 cve-icon cve-icon
https://github.com/element-hq/synapse/security/advisories/GHSA-fh66-fcv5-jjfr cve-icon cve-icon
History

Wed, 15 Oct 2025 16:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Thu, 09 Oct 2025 13:00:00 +0000

Type Values Removed Values Added
First Time appeared Element-hq
Element-hq synapse
Vendors & Products Element-hq
Element-hq synapse

Wed, 08 Oct 2025 15:15:00 +0000

Type Values Removed Values Added
Description Synapse is an open source Matrix homeserver implementation. 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. The issue is 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, the maintainers of Synapse recommend skipping these releases and upgrading straight to 1.138.4 and 1.139.2.
Title Synapse: Invalid device keys degrade federation functionality
Weaknesses CWE-1287
References
Metrics cvssV4_0

{'score': 5.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N'}
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2025-10-08T14:55:06.378Z

Updated: 2025-10-15T16:11:07.284Z

Reserved: 2025-09-29T20:25:16.180Z

Link: CVE-2025-61672

cve-icon Vulnrichment

Updated: 2025-10-08T15:20:42.340Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2025-10-08T15:16:25.110

Modified: 2025-10-08T19:38:09.863

Link: CVE-2025-61672

cve-icon Redhat

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