Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. If Synapse and a malicious homeserver are both joined to the same room, the malicious homeserver can trick Synapse into accepting previously rejected events into its view of the current state of that room. This can be exploited in a way that causes all further messages and state changes sent in that room from the vulnerable homeserver to be rejected. This issue has been patched in version 1.68.0
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Synapse | Matrix | 1.62.0 (including) | 1.68.0 (excluding) |
| Matrix-synapse | Ubuntu | bionic | * |
| Matrix-synapse | Ubuntu | esm-apps/focal | * |
| Matrix-synapse | Ubuntu | esm-apps/jammy | * |
| Matrix-synapse | Ubuntu | focal | * |
| Matrix-synapse | Ubuntu | jammy | * |
| Matrix-synapse | Ubuntu | kinetic | * |
| Matrix-synapse | Ubuntu | lunar | * |
| Matrix-synapse | Ubuntu | mantic | * |
| Matrix-synapse | Ubuntu | trusty | * |
| Matrix-synapse | Ubuntu | upstream | * |
| Matrix-synapse | Ubuntu | xenial | * |
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.