The lab has changed one configuration file that belongs to one of the packages logrotate, sudo, or the OpenSSH client (openssh-clients on the RHEL family, openssh-client on Ubuntu), for you to find in task 2. Write answers to the files in /root/lab-answers/.

Do task 1's test as your own login user (not root), from your SSH or console session, so that the audit system knows who you are.

Tasks

Install the audit tools if they're missing (audit-rules on the RHEL family, auditd on Ubuntu). Add two audit rules, permanently, with a file in /etc/audit/rules.d/ and augenrules: a watch on /etc/hosts for writes and attribute changes with the key hosts-change, and a rule, key access-denied, for openat calls that fail with EACCES by users with a login UID of 1000 or more. Then change /etc/hosts (and put it back), try to read /etc/shadow as your login user, and find both events with ausearch.
Find the changed file with your package manager's verify function, and write its full path to /root/lab-answers/2.
Install AIDE and write your own configuration, /root/aide/lab.conf, that reads the database from /root/aide/aide.db, writes new ones to /root/aide/aide.db.new, uncompressed, and covers /etc/ssh and /usr/sbin with permissions, owner, group, size, mtime and SHA-256. Build the database as /root/aide/aide.db. Plant a file in /usr/sbin, change a file in /etc/ssh, see AIDE report both, and put things back.
Schedule that check nightly at 3:30 with a file in /etc/cron.d, mailing its output to root.
RHEL family: evaluate the CIS Level 1 server profile's rules package_aide_installed and sshd_disable_root_login with oscap, saving the results to /root/oscap-results.xml.
Ubuntu: install chkrootkit, rkhunter and debsums, record rkhunter's baseline of file properties, and run both scanners.

Hints

auditctl -w PATH -p wa -k KEY; -a always,exit -F arch=b64 -S openat -F exit=-EACCES -F 'auid>=1000' -F auid!=unset -k KEY; augenrules --load, auditctl -l; ausearch -k KEY -i, -f FILE, aureport -k --summary.
rpm -Va or rpm -V PACKAGE; dpkg --verify, debsums -as.
database_in=file:..., database_out=file:..., gzip_dbout=no, a rule line such as LabRule = p+u+g+s+m+sha256, then /etc/ssh LabRule; aide --init -c FILE, aide --check -c FILE.
MAILTO=root, then minute hour day month weekday user command.
/usr/share/xml/scap/ssg/content/ (pick the data stream for your distribution); oscap info --profiles; oscap xccdf eval --profile ... --rule xccdf_org.ssgproject.content_rule_NAME --results FILE.
apt-get install --no-install-recommends; rkhunter --propupd, rkhunter --check --sk, chkrootkit -q; /var/log/rkhunter.log.