How to whitelist IP addresses for ModSecurity in Plesk?

Question

How to whitelist a single/multiple IP addresses for ModSecurity in Plesk?

Answer

1. Connect to the server via SSH.

2. Create/ open for editing ModSecurity file that is used for IP whitelisting:

   For Debian based systems (Ubuntu/Debian):

   # vi /etc/apache2/modsecurity.d/000ipwhitelist.conf

   For RHEL based systems (CentOS/CloudLinux):
   

   # vi /etc/httpd/conf/modsecurity.d/rules/000ipwhitelist.conf

3. Add the following rule in 1 line there:

   SecRule REMOTE_ADDR "@ipMatch 203.0.113.0/24,192.0.2.2" "id:3,phase:1,t:none,log,pass,ctl:ruleRemoveById=55666"

   Where:
   55666 – is the existing ModSecurity Rule and it should be replaced with the required rule ID.
   203.0.113.0/24 – IP addresses that required to whitelist. Multiple, comma-separated, addresses can be also specified.  

4. Check Apache syntax:

   For Debian based systems (Ubuntu/Debian):
   

   # apache2ctl -t

   For RHEL based systems (CentOS/CloudLinux):
   

   # httpd -t

5. If syntax is not OK, fix it. If it is OK, apply the new configuration:

   For Debian based systems (Ubuntu/Debian):
   

   # service apache2 reload

   For RHEL based systems (CentOS/CloudLinux):
   

   # service httpd reload

Note: Whitelist rules should be placed before other rules.
For details see: https://www.modsecurity.org/CRS/Documentation/exceptions.html 
https://github.com/SpiderLabs/ModSecurity/wiki/Reference-Manual-%28v2.x%29#ipMatch