Yes. The default tablespace assigned to user is USERS and not SYSTEM, temp tablespace is TEMP

But if user executes

create table test (id number) tablespace system it gets created in system tablespace

The way we allocate quota on tablespace, Is there is any to stop them by allocating 0 quota on system tablespace.

I tried

alter user xxxx quota 0 on system

it works.. but still user able to create table in SYSTEM tablespace...

How do I stop this??