Information
The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to increase exponentially the time and/or resources required to compromise the password.
RHEL 9 uses 'pwquality' as a mechanism to enforce password complexity. Configurations are set in the 'etc/security/pwquality.conf' file.
The 'minlen', sometimes noted as minimum length, acts as a 'score' of complexity based on the credit components of the 'pwquality' module. By setting the credit components to a negative value, not only will those components be required, but they will not count toward the total 'score' of 'minlen'. This will enable 'minlen' to require a 15-character minimum.
The DOD minimum password requirement is 15 characters.
Solution
Configure RHEL 9 to enforce a minimum 15-character password length.
Add the following line to '/etc/security/pwquality.conf' (or modify the line to have the required value):
minlen = 15