What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.3 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-10-08 · updated 2026-10-08
• Weakness: CWE-1287

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.

Affected products

• matrix-org synapse: before 1.138.3; = 1.139.0

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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