Parse Server before 8.6.98 and 9.0.0 before 9.10.3 does not enforce the create and addField class-level permissions of the _Session class when creating sessions. An authenticated user, or anyone holding that user's session token, can send POST requests to /sessions or /classes/_Session to create additional sessions for that user and add fields to _Session; these sessions are not revoked when the original session is logged out.