Bug 2402525 (CVE-2025-61672)

Summary: CVE-2025-61672 matrix-synapse: Synapse: Lack of device key validation leads to federation degradation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: low    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Synapse, an open source Matrix homeserver implementation. This vulnerability allows an attacker registered on the victim homeserver to degrade federation functionality, unpredictably breaking outbound federation to other homeservers via lack of validation for device keys.
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Description OSIDB Bzimport 2025-10-08 16:01:18 UTC
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.