CVE-2025-61672
October 08, 2025
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 Packages
https://github.com/element-hq/synapse.git (GITHUB):
Affected version(s) =v1.139.0 <v1.139.1Fix Suggestion:
Update to version v1.139.1https://github.com/element-hq/synapse.git (GITHUB):
Affected version(s) >=v1.0.0 <v1.138.3Fix Suggestion:
Update to version v1.138.3matrix-synapse (PYTHON):
Affected version(s) >=1.139.0rc2 <1.139.1Fix Suggestion:
Update to version 1.139.1matrix-synapse (PYTHON):
Affected version(s) >=0.33.5 <1.138.3Fix Suggestion:
Update to version 1.138.3Related Resources (10)
Do you need more information?
Contact UsCVSS v4
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
LOW
Vulnerable System Availability
LOW
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
5.4
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
LOW
Weakness Type (CWE)
Improper Validation of Specified Type of Input
EPSS
Base Score:
0.06
