Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Prior to 9.6.0-alpha.9 and 8.6.35, an attacker can exploit LiveQuery subscriptions to infer the values of protected fields without directly receiving them. By subscribing with a WHERE clause that references a protected field (including via dot-notation or $regex), the attacker can observe whether LiveQuery events are delivered for matching objects. This creates a boolean oracle that leaks protected field values. The attack affects any class that has both protectedFields configured in Class-Level Permissions and LiveQuery enabled. This vulnerability is fixed in 9.6.0-alpha.9 and 8.6.35.