Passwords must be prohibited from reuse for a minimum of five generations.

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Associated with: CCI-000200

SV-90155r2_rule Passwords must be prohibited from reuse for a minimum of five generations.

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.

Check content

Verify that 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 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 text

Configure the Ubuntu operating system prevents 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 remember=5 rounds=5000

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