$ sudo apt-get update
$ sudo apt-get install apache2-suexec-custom 

apache2-suexec-custom is installed in your system.

Make ensure the apache2-suexec-custom package were installed using the commands given below,

$ sudo dpkg-query -l | grep apache2-suexec-custom *

You will get with apache2-suexec-custom package name, version, architecture and description in a table

apache2-suexec-custom package basic information: