Vulnerability Discussion

Ensuring shells are not given to system accounts upon login makes it more difficult for attackers to make use of system accounts.

Check

Verify that system accounts must not have an interactive login shell with the following command:

$ awk -F: '($3<1000){print $1 ":" $3 ":" $7}' /etc/passwd

root:0:/bin/bash
bin:1:/sbin/nologin
daemon:2:/sbin/nologin
adm:3:/sbin/nologin
lp:4:/sbin/nologin
sync:5:/bin/sync
shutdown:6:/sbin/shutdown
halt:7:/sbin/halt
mail:8:/sbin/nologin
operator:11:/sbin/nologin
games:12:/sbin/nologin
ftp:14:/sbin/nologin
systemd-coredump:999:/sbin/nologin
dbus:81:/sbin/nologin
polkitd:998:/sbin/nologin
tss:59:/sbin/nologin
sssd:997:/sbin/nologin
unbound:996:/sbin/nologin
fapolicyd:995:/sbin/nologin
postfix:89:/sbin/nologin
sshd:74:/sbin/nologin
chrony:994:/sbin/nologin
systemd-oom:989:/usr/sbin/nologin

Identify the system accounts from this listing that do not have a nologin shell.

If any system account (other than the root account) has a login shell and it is not documented with the information system security officer (ISSO), this is a finding.

Fix

Configure AlmaLinux OS 9 so that all noninteractive accounts on the system do not have an interactive shell assigned to them.

If the system account needs a shell assigned for mission operations, document the need with the ISSO.

Run the following command to disable the interactive shell for a specific noninteractive user account, replacing <user> with the user that has a login shell.

$ usermod --shell /sbin/nologin <user>

Do not perform the steps in this section on the root account. Doing so will cause the system to become inaccessible.