ORA-65066: The specified changes must apply to all containers - ORACLE 12 C

SQL> CONN system/oracle@pdb1
Connected.
SQL> alter user system identified by oracle12;
alter user system identified by oracle12
*
ERROR at line 1:
ORA-65066: The specified changes must apply to all containers


Connect to CDB database ,Then you can reset the system user then it will applies to all PDB's as well.

SQL> conn sys as sysdba
Enter password:
Connected.
SQL> alter user system identified by oracle12;

User altered.

SQL> CONN system/oracle12@pdb1
Connected.

SQL> SHOW CON_NAME

CON_NAME
------------------------------
PDB1