get own session serial# without privilege

[oracle@stormking cdb12201 sqlplus]$ sqlplus /nolog @ conn.pdba.u.sql

SQL*Plus: Release 12.2.0.1.0 Production on Fri Jul 7 01:56:21 2017

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected.
SQL> create user r identified by r;

User created.

SQL> grant create session to r;

Grant succeeded.

SQL> conn r/r@stormking:1521/pdba
Connected.
SQL> select sid, serial# from v$session_connect_info where sid = sys_context( 'userenv', 'sid' ) and rownum = 1;

       SID    SERIAL#
---------- ----------
        25       1457