Cross-principal document update, theft, and deletion via unvalidated id in nested attributes

An insecure direct object reference in the nested attributes handling of the Mongoid object-document mapper may allow a user with basic application privileges to reference a record identifier that is not their own. Processing such a request can cause that record to be looked up without the usual ownership or scoping restrictions, then updated and linked to the requesting user's own record. This may result in unintended disclosure and unauthorized modification of data belonging to other users of the application.