Medium 5.3Published Oct 8, 2025

CVE-2025-61672Synapse: Invalid device keys degrade federation functionality

Updated under an hour ago (Oct 26, 2026, 8:23 AM ET)

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No exploitation reported and no EPSS estimate yet.

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Every CVE for element-hq synapse

Exploited in the last 30 days

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.

CVSS: 5.3 MEDIUM (v4.0, CNA)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
Weakness (CWE): CWE-1287
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Oct 15, 2025
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

element-hq synapse element_hq:synapse (from the name)	before 1.138.3; = 1.139.0	CNA record

References

https://github.com/element-hq/synapse/security/advisories/GHSA-fh66-fcv5-jjfrx-refsource-confirm
https://github.com/element-hq/synapse/pull/17097x-refsource-misc
https://github.com/element-hq/synapse/commit/26aaaf9e48fff80cf67a20c691c75d670034b3c1x-refsource-misc
https://github.com/element-hq/synapse/commit/7069636c2d6d1ef2022287addf3ed8b919ef2740x-refsource-misc
https://github.com/element-hq/synapse/releases/tag/v1.138.3x-refsource-misc
https://github.com/element-hq/synapse/releases/tag/v1.139.1x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.