You should properly secure the databases, platforms, and servers that you use for P6 EPPM. You might find the links below helpful when planning your security strategy (not a comprehensive list).
Note: The URLs below might have changed after Oracle published this guide.
Oracle Database
http://download.oracle.com/docs/cd/B19306_01/network.102/b14266/toc.htm
Oracle Linux Security Guide
http://www.oracle.com/technetwork/articles/servers-storage-admin/secure-linux-env-1841089.html
Microsoft SQL Server 2014 SP1 Database
https://www.microsoft.com/en-us/server-cloud/products/sql-server/Resources.aspx
Microsoft Windows 2012 R2 Server
https://www.microsoft.com/en-us/server-cloud/products/sql-server-editions/overview.aspx
Oracle WebLogic
http://www.oracle.com/technetwork/middleware/weblogic/documentation/index.html
http://download.oracle.com/docs/cd/E12840_01/wls/docs103/secmanage/ssl.html
Oracle Fusion Middleware Security Guides
http://download.oracle.com/docs/cd/E12839_01/security.htm