cracklib pam module is method to check the password against dictionary list and gives you availability to check the strength of the password and set rules to identify the poor passwords
here is the most important parameters for this module
- minlen minimal password length
- dcredit maximum number of digits
- ucredit maximum upper case letters
- lcredit maximum lower case letters
- ocredit maximum other letters not similer to the old one
- maxrepeat limit repeated letters
- reject_username check if the username inside the password to avoid this week accounts bob/bob or bob/bob123
- enforce_for_root this is the most important one , why ? , because if you didn’t apply it users will just notice the warrning and whatever password will be applied with the parameter will force the use to use our policy 😉
- dicpath set crack lib dictionary to specific passwords database base i recommend (rockyyou) database coz it contains many leaked passwords and used by many attackers to bruteforce the system example dicpath=/var/wordlist/rockyyou.txt
time to deploy our password policy
we want to apply this for new password also we can force the users to update their passwords once they do login via this command
for user in $(grep "/bin/bash" /etc/passwd|cut -d ":" -f1);do chage -d 0 $user;done
this command have high impact it will find all users with bash shell and force them to update the password even the root u can exclude the root by piping the output from grep and use grep -v root
You are required to change your password immediately (root enforced)
Last login: Mon Aug 3 19:55:51 2015 from 192.168.72.1
WARNING: Your password has expired.
You must change your password now and login again!
Changing password for user n1x.
Changing password for n1x.
(current) UNIX password:
Retype new password:
passwd: all authentication tokens updated successfully.
Connection to cbox closed.
we will use the passwd module inside /etc/pam.d/passwd
to add our new policy
auth include system-auth
account include system-auth
password substack system-auth
-password optional pam_gnome_keyring.so
pssword required pam_cracklib.so dcredit=1 ucredit=1 ocredit=1 lcredit=1 minlen=8 enforce_for_root
here is the output of different failed password change
BAD PASSWORD: is too similar to the old one
BAD PASSWORD: it is based on a dictionary word
BAD PASSWORD: it is based on a (reversed) dictionary word
BAD PASSWORD: it is too short