NixOS must enforce the limit of three consecutive invalid logon attempts by a user during a 15-minute time period.

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

Satisfies: SRG-OS-000021-GPOS-00005, SRG-OS-000329-GPOS-00128, SRG-OS-000470-GPOS-00214

Verify that NixOS locks an account after three unsuccessful logon attempts within 15 minutes with the following commands:

$ cat /etc/pam.d/login

auth required pam_faillock.so preauth deny=3 even_deny_root fail_interval=900 unlock_time=0 dir=/var/log/faillock

If the "fail_interval" option is not set to "900" or less (but not "0") on the "preauth" lines with the "pam_faillock" module, or is missing from this line, this is a finding.

Configure NixOS to lock an account when three unsuccessful logon attempts occur within 15 minutes.

Update the NixOS config, typically stored either in /etc/nixos/configuration.nix or /etc/nixos/flake.nix, to include the following lines:

security.pam.services = let pamfile = '' auth required pam_faillock.so preauth silent audit deny=3 fail_interval=900 unlock_time=0 auth sufficient pam_unix.so nullok try_first_pass auth [default=die] pam_faillock.so authfail audit deny=3 fail_interval=900 unlock_time=0 auth sufficient pam_faillock.so authsucc

account required pam_faillock.so ''; in { login.text = pkgs.lib.mkDefault pamfile; sshd.text = pkgs.lib.mkDefault pamfile; };

Note that the entire pam file must be entered as this pamfile string.

Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch