Information
The minimum password age determines the number of weeks that you must use a password before you can change it.
Users may have favorite passwords that they like to use because they are easy to remember and they believe that their password choice is secure from compromise.Unfortunately, passwords are compromised and if an attacker is targeting a specific individual user account, with foreknowledge of data about that user, reuse of old, potentially compromised passwords, may cause a security breach.By restricting the frequency of password changes, an administrator can prevent users from repeatedly changing their password in an attempt to circumvent password reuse controls
Solution
In /etc/security/user set the default user stanza minage attribute to 1 :
chsec -f /etc/security/user -s default -a minage=1
This means that a user can only change their password after one week.
Impact:
By enforcing a minimum password age, a user will be unable to change their password if they observe a potential compromise of their password, e.g. "shoulder surfing", during the time defined by minimum password age. In this event the user should follow local site policy to report a compromised password.
If a users password is set by other personnel as a procedure in dealing with a lost or expired password, the user should be forced to update this "set" password with their own password. e.g. use the ADMINCHG flag on the account.
If it is not possible to have a user set their own password immediately, and this recommendation or local site procedure may cause a user to continue using a third party generated password, minage for the affected user should be temporally changed to 0, to allow a user to change their password immediately.
For applications where the user is not using the password at console, the ability to "change at next logon" may be limited. This may cause a user to continue to use a password created by other personnel.
The AIX community prefers to rely on the AIX attribute histexpire rather than a historical minage value as this better satisfies the need to prevent cycling through passwords. The CIS Password Policy still recommends the use of a minimum age, hence the retention of this recommendation at level 2.