title: Synapse vulnerable to denial of service (DoS) due to incorrect application of event authorization rules
description: Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. The Matrix specification specifies a list of [event authorization rules](https://spec.matrix.org/v1.2/rooms/v9/#authorization-rules) which must be checked when determining if an event should be accepted into a room. In versions of Synapse up to and including version 1.61.0, some of these rules are not correctly applied. An attacker could craft events which would be accepted by Synapse but not a spec-conformant server, potentially causing divergence in the room state between servers. Administrators of homeservers with federation enabled are advised to upgrade to version 1.62.0 or higher. Federation can be disabled by setting [`federation_domain_whitelist`](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#federation_domain_whitelist) to an empty list (`[]`) as a workaround.
problem types: CWE-703: Improper Check or Handling of Exceptional Conditions
affected:
{
product: synapse
vendor: matrix-org
versions:
status: affected, version: < 1.62.0
}
metrics:
cvssV3_1: [
attackComplexity: HIGH
attackVector: NETWORK
availabilityImpact: HIGH
baseScore: 6.4
baseSeverity: MEDIUM
confidentialityImpact: LOW
integrityImpact: LOW
privilegesRequired: LOW
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
version: 3.1
]