Information
The PASSWORD_VERIFY_FUNCTION enforces password complexity checks when a database account's password is changed. It should be set for all profiles.
Note that this setting does not apply to administrative roles (like SYSDBA, SYSDG or SYSOPER) authenticated by the Oracle password file. From 12.2, Oracle provides password complexity rules for password file users (Doc 2294754.1)
Through Oracle Database profiles, password complexity rules (mixed cases with digits and special characters), blocking of simple combinations, and enforcing change/history settings can potentially thwart unauthorized logins by an unauthorized user.
Solution
Use the password verification function, or create a custom password verification function which fulfills the password requirements of the organization.
Oracle supplies two password verification functions with the database ora12c_verify_function and ora12c_strong_verify_function You may also create your own function if your organization's standards are different from the functions Oracle supplies. For a sample of a password verification function that you can customize to meet your needs, see $ORACLE_HOME/rdbms/admin/catpvf.sql In most cases, we recommend that ora12c_strong_verify_function be used.