Synapse is an open-source Matrix homeserver. A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in the V2 state resolution algorithm. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service. Servers in private federations, or those that do not federate, are not affected. Server administrators should upgrade to 1.105.1 or later. Some workarounds are available. One can ban the malicious users or ACL block servers from the rooms and/or leave the room and purge the room using the admin API.
CVSS Details
- CVSS 3.1 Base Score: 6.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alpine Linux | — | Upgrade synapse | Aug 22, 2024 | Apr 23, 2024 |
| Freebsd | — | Upgrade py39-matrix-synapseUpgrade py311-matrix-synapseUpgrade py310-matrix-synapseUpgrade py38-matrix-synapse | Dec 10, 2025 | Apr 24, 2024 |
| Ubuntu | — | Upgrade matrix-synapse (Ubuntu Pro) | Apr 24, 2025 | Apr 23, 2024 |
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