https://docs.oracle.com/cd/E66029_01/doc.732/e66033/sec_overview.htm#ITGSC108 Basic Security Considerations The following principles are fundamental to using any application securely:
Keep software up to date. This includes the latest product release and any patches that apply to it.
Limit privileges as much as possible. Users should be given only the access necessary to perform their work. User privileges should be reviewed periodically to determine relevance to current work requirements.
Monitor system activity. Establish who should access which system components, how often they should be accessed, and who should monitor those components.
Install software securely. For example, use firewalls, secure protocols (such as SSL), and secure passwords. See "Performing a Secure Network Integrity Installation" for more information.
Learn about and use Network Integrity security features. See "Implementing Network Integrity Security" for more information.
Use secure development practices. For example, take advantage of existing database security functionality instead of creating your own application security. See "Security Considerations for Developers" for more information.
Keep up to date on security information. Oracle regularly issues security-related patch updates and security alerts. You must install all security patches as soon as possible from the Oracle Technology Network web site:
http://www.oracle.com/technetwork/topics/security/alerts-086861.html

https://docs.cloud.oracle.com/en-us/iaas/Content/Database/Tasks/configuringDB.htm