SLEM 5 must lock an account after three consecutive invalid access attempts.

By limiting the number of failed access attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.

The pam_tally2.so module maintains a count of attempted accesses. This includes username entry into a logon field as well as password entry. With counting access attempts, it is possible to lock an account without presenting a password into the password field. This should be taken into consideration as it poses as an avenue for denial of service (DoS).

Verify SLEM 5 locks a user account after three consecutive failed access attempts until the locked account is released by an administrator with the following command:

     > grep pam_tally2.so /etc/pam.d/common-auth 
     auth required pam_tally2.so onerr=fail deny=3 

If "deny" set to a value other than "1", "2", or "3", if "onerr=fail" is missing, if the line is commented out, or the line is missing, this is a finding.

Configure SLEM 5 to lock an account when three unsuccessful access attempts occur.

Note: Manual changes to the listed files may be overwritten by the "pam-config" program. The "pam-config" program should not be used to update the configurations listed in this requirement.

Add or modify the first line of the auth section in the "/etc/pam.d/common-auth" file to match the following line:

auth required pam_tally2.so onerr=fail silent audit deny=3

Add or modify the following line in the "/etc/pam.d/common-account" file:

account required pam_tally2.so