linuxexpert-practice-labs/labs/linux-plus/3-3-1-sudo-and-su

Linux+ 3.3.1: sudo and su

A sudo rule for one command, finding a refused command in the log, and closing a shell escape with NOEXEC.

Before you start

The lab makes the journal persistent if it isn't, so the log of task 2 survives a reboot. User sudotest doesn't exist yet: you create it.

Tasks

1. Look at your own rights (sudo -l) and at /etc/sudoers and what it includes. Then create user sudotest with the password Lab-Pass-123, and a file /etc/sudoers.d/sudotest that lets it run, as root, only systemctl status sshd and systemctl status ssh. Give the file mode 440 and check the sudo configuration with visudo -c.
2. As sudotest, list your rights, check the SSH service's status with sudo, and try sudo id, which is refused. Find the refusal in the journal.
3. Also let sudotest run /usr/bin/less /etc/shadow as root, keeping the rule from task 1. Try it and type !id in less: you get a root shell command. Then change the rule to use NOEXEC, so that the shell escape is refused.

Hints

• useradd -m, chpasswd; ALL=(root) /usr/bin/systemctl status sshd, ...; chmod 440; visudo -c.
• su - sudotest, sudo -l; journalctl _COMM=sudo --since "10 min ago".
• One rule can list several commands, or use one line per command; NOEXEC: goes before the command it applies to.