apache2-mpm-itk is an MPM (Multi-Processing Module) for the Apache web server. mpm-itk allows you to run each of your vhost under a separate uid and gid — in short, the scripts and configuration files for one vhost no longer have to be readable for all the other vhosts.
1. Install the apache2-mpm-itk package
apt-get install apache2-mpm-itk
2. Configure user and group for each virtual host by adding the following line somewhere between <VirtualHost *:80>…</VirtualHost>
AssignUserId [user] [group]
Replace [user] and [group] with a username and group name that already exists on the system.
3. Change the owner of the web root
chown [user].[group] [location]
Replace [user] and [group] with the username and group name configured on the virtual host. Replace [location] with the location specified as DocumentRoot for the virtual host, eg. /var/www
4. Make sure the location isn’t accessible by other users (optional)
chmod o= [location]
Replace [location] with the location specified as DocumentRoot for the virtual host, eg. /var/www
5. Restart apache