Oracle 12c default sys password
If you are on the same system where Oracle database is installed and you have logged in to the system using a correct privileged user then you can bypass the password.


  Please note that the path of the ORACLE_HOME and ORACLE_SID is
  properly configured. Also, TNSLISTNER and SQLNET files are properly
  configured.


You can directly log into DB as a sysdba using the following command:

sqlplus / as sysdba