Cis Ubuntu1804 V220 1 2 2

1.2.2 Ensure filesystem integrity is regularly checked (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

Periodic checking of the filesystem integrity is needed to detect changes to the filesystem.

Rationale

Periodic file checking allows the system administrator to determine on a regular basis if critical files have been changed in an unauthorized fashion.

Audit Procedure

Command Line

Run the following commands to verify a cron job scheduled to run the aide check:

grep -Prs '^([^#\n\r]+\h+)?(\/usr\/s?bin\/|^\h*)aide(\.wrapper)?\h+(--check|([^#\n\r]+\h+)?\$AIDEARGS)\b' /etc/cron.* /etc/crontab /var/spool/cron/

Ensure a cron job in compliance with site policy is returned.

OR

Run the following commands to verify that aidecheck.service and aidecheck.timer are enabled and aidecheck.timer is running:

systemctl is-enabled aidecheck.service
systemctl is-enabled aidecheck.timer
systemctl status aidecheck.timer

Expected Result

A cron job or systemd timer configured to run AIDE checks regularly.

Remediation

Command Line

If cron will be used to schedule and run aide check:

crontab -u root -e

Add the following line to the crontab:

0 5 * * * /usr/bin/aide.wrapper --config /etc/aide/aide.conf --check

OR If aidecheck.service and aidecheck.timer will be used to schedule and run aide check:

Create or edit the file /etc/systemd/system/aidecheck.service and add the following lines:

[Unit]
Description=Aide Check

[Service]
Type=simple
ExecStart=/usr/bin/aide.wrapper --config /etc/aide/aide.conf --check

[Install]
WantedBy=multi-user.target

Create or edit the file /etc/systemd/system/aidecheck.timer and add the following lines:

[Unit]
Description=Aide check every day at 5AM

[Timer] 05:00:00
Unit=aidecheck.service

[Install]
WantedBy=multi-user.target

Run the following commands:

chown root:root /etc/systemd/system/aidecheck.*
chmod 0644 /etc/systemd/system/aidecheck.*
systemctl daemon-reload
systemctl enable aidecheck.service
systemctl --now enable aidecheck.timer

Additional Information

The checking in this recommendation occurs every day at 5am. Alter the frequency and time of the checks in compliance with site policy.

systemd timers, timer file aidecheck.timer and service file aidecheck.service, have been included as an optional alternative to using cron.

Ubuntu advises using /usr/bin/aide.wrapper rather than calling /usr/bin/aide directly in order to protect the database and prevent conflicts.

References

1. https://github.com/konstruktoid/hardening/blob/master/config/aidecheck.service
2. https://github.com/konstruktoid/hardening/blob/master/config/aidecheck.timer
3. NIST SP 800-53 Rev. 5: AU-2

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