Firebase security rules are server-side configurations that control read and write operations to your database. They use a custom, JSON-like language and can be set in the Firebase console or by deploying from local files using Firebase CLI.
To prevent unauthorized access, you would structure your rules based on user authentication status and data paths. For example:
{ "rules": {".read": "auth != null",".write": "auth != null" }}
This rule restricts both reading and writing to authenticated users only. You could also specify more granular permissions based on user IDs or other attributes stored in the auth token.
Remember, Firebase evaluates rules in order, so place more specific rules before general ones. Also, any read or write operation that isn’t explicitly allowed is denied.