Ubuntu OS must store only encrypted representations of passwords.

Passwords must be protected at all times and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. If the application allows the user to consecutively reuse their password when that password has exceeded its defined lifetime, the end result is a password that is not changed as per policy requirements.

Verify the Ubuntu operating stores only encrypted representations of passwords with the following command:

     $ grep pam_unix.so /etc/pam.d/common-password 
     password [success=1 default=ignore] pam_unix.so obscure sha512 shadow remember=5 rounds=100000

If "sha512" is missing from the "pam_unix.so" line, this is a finding.

Configure Ubuntu OS to store encrypted representations of passwords.

Add or modify the following line in the "/etc/pam.d/common-password" file:

password [success=1 default=ignore] pam_unix.so obscure sha512 shadow remember=5 rounds=100000