CVE-2025-61672
CVE-2025-61672 is a medium-severity vulnerability with a CVSS 4.0 base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1287.
Key facts
- Severity: Medium (CVSS 4.0 base score 5.3)
- EPSS exploit prediction: 0% (35th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2025-33305
- Weakness: CWE-1287
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2025-61672?
- 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.
- How severe is CVE-2025-61672?
- CVE-2025-61672 has a CVSS 4.0 base score of 5.3, rated medium severity.
- Is CVE-2025-61672 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2025-61672?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2025-61672 have an EU (EUVD) identifier?
- Yes. CVE-2025-61672 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-33305.
- When was CVE-2025-61672 published?
- CVE-2025-61672 was published on 2025-10-08 and last updated on 2026-06-17.
References
- https://github.com/element-hq/synapse/commit/26aaaf9e48fff80cf67a20c691c75d670034b3c1
- https://github.com/element-hq/synapse/commit/7069636c2d6d1ef2022287addf3ed8b919ef2740
- https://github.com/element-hq/synapse/pull/17097
- https://github.com/element-hq/synapse/releases/tag/v1.138.3
- https://github.com/element-hq/synapse/releases/tag/v1.139.1
- https://github.com/element-hq/synapse/security/advisories/GHSA-fh66-fcv5-jjfr
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