Vulnerability Discussion

Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. If the information system or 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.

Satisfies: SRG-OS-000077-GPOS-00045, SRG-OS-000073-GPOS-00041

Check

Verify the Ubuntu operating system prevents passwords from being reused for a minimum of five generations by running the following command:

$ grep -i remember /etc/pam.d/common-password

password [success=1 default=ignore] pam_unix.so obscure sha512 shadow remember=5 rounds=5000

If the "remember" parameter value is not greater than or equal to "5", is commented out, or is not set at all, this is a finding.

Fix

Configure the Ubuntu operating system to prevent passwords from being reused for a minimum of five generations.

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

password [success=1 default=ignore] pam_unix.so obscure sha512 shadow remember=5 rounds=5000