When executed a sql on system dictionary, the error ORA-609 was raised along with "can not execute recursive sql".

1. Check the current session opened cursors with following sql.

select a.value, s.username, s.sid, s.serial# from v$sesstat a, v$statname b, v$session s where a.statistic# = b.statistic# and s.sid=a.sid and b.name = 'opened cursors current';

     VALUE USERNAME                              SID    SERIAL#
---------- ------------------------------ ---------- ----------
         0                                         1          1
         0                                         2          1
         0                                         3          1
         0                                         4          1
         0                                         5          5
         0                                         7          1
         1                                         9      16864
        12 DBSNMP                                 10      15572
         1 SYS                                    16      27185
        56 SYSMAN                                 17      22626
         5 SYSMAN                                 18      20353
       300 CUSRGL                                 22       6188
         0                                        63          7
         0                                        64          1
         0                                        65          1
         1                                        66          1

2. Check the system parameters
SQL> show parameters cursor

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cursor_sharing                       string      EXACT
cursor_space_for_time                boolean     FALSE
open_cursors                         integer     300
session_cached_cursors               integer     50

We can see that session 22 reached the max limit of open cursors.