Install ModSecurity Plesk

The following options are possible (GUI/CLI):

via Plesk GUI

go to Home > Tools & Settings > Updates and Upgrades:

Add/Remove Components:

and under the web hosting settings select ModSecurity:

Installed:

via CLI

execute plesk installer

# plesk installer

CLI Installer

The Plesk Installation and Upgrade Wizard will guide you through
the installation or upgrade process.
===============================================================================

------ IMPORTANT ------

* New installation of product(s) should be performed on clean servers only.

* Before upgrading Plesk, be sure to back up your data.

* By using this Wizard you agree to the terms and conditions described at
  http://www.plesk.com/legal/terms/ and those of the Plesk End User
  License Agreement.

Available actions:
(F) Go forward
(Q) Cancel installation

Select an action [F/q]: F

Select Go forward (F)

Select the products to install and their versions
===============================================================================

The following product versions are available:

1. [*] Plesk
  2. (*) Plesk Onyx 17.0.17 (currently installed)

Available actions:
(F) Go forward
(B) Go back
(Q) Cancel installation
(S) Show advanced settings

Select an action or a number [F/b/q/s/1-2]: F

Select Go forward (F)

Main components list for Plesk
===============================================================================

 26 of 53 components selected

Please select the components of Plesk you want to install:

 1. [=] Plesk
 2. [=] BIND DNS server
 3. [ ] PostgreSQL server
 4. [ ] Server Health Monitor
 5. [ ] Fail2Ban
 6. [=] All language localization for Plesk
 7. [=] Git
 8. [=] Docker
 9. [=] Resource controller based on Systemd
10. [ ] Plesk Migrator
11. [ ] Web Presence Builder
12. [=] MySQL server
13. [=] <+> Webmail services // 2 of 2 components selected
14. [.] <+> Mail hosting // 2 of 6 components selected
15. [.] <+> Web hosting // 10 of 22 components selected
16. [.] <+> Plesk extensions // 5 of 11 components selected

Enter a number to toggle the respective component or view the group (marked with <+>).

Available actions:
(F) Go forward
(B) Go back
(Q) Cancel installation
(A) Select all
(D) Deselect all

Select an action or a number [F/b/q/a/d/1-16]: 15

and under Select the components you want to install menu select Web hosting (15)

Primary components list / hosting
===============================================================================

Select the components you want to install:
 1. [=] ProFTPD
 2. [ ] Support for Tomcat Java Servlets
 3. [=] Webalizer
 4. [=] AWStats
 5. [=] ModSecurity
 6. [ ] Phusion Passenger server
 7. [ ] Ruby support
 8. [ ] NodeJS support
 9. [ ] Tools required for building Ruby gems
10. [.] <+> Apache // 2 of 5 components selected
11. [.] <+> PHP interpreter versions // 3 of 7 components selected
12. [=] <+> Nginx web server and reverse proxy server // 1 of 1 components selected

Enter a number to toggle the respective component or view the group (marked with <+>).

Available actions:
(B) Go back
(Q) Cancel installation
(A) Select all
(D) Deselect all

Select an action or a number [B/q/a/d/1-12]: 6

and then ModSecurity (6)

Then go to back Main components list for Plesk and Select F (Go Forward)

Preparing Your System for Product Installation
===============================================================================

There are 1 packages required for the product to function properly which
were not found in your system.

There are 1 packages that need to be upgraded
in order to install the product.


Available actions:
(F) Go forward
(B) Go back
(Q) Cancel installation
(S) Show the list of packages

Select an action [F/b/q/s]:  F

Then installation finnished!