default user privileges

 I have created a user and a role. I granted the select permission of about 6 tables in a schema to the role and than granted the role to the user. However, somehow the user is able to access some of tables in other schema as well as system tables such as sys.audit_action etc. Since I all I did was assign user the default profile, grant create session, and grant the role, I am kind of wondering if by default the user gets to access the system table?