Directory listing is enable by default on cPanel, if you’re not put any index file (index.html, index.htm, index.php, etc.) on any folder in any accounts, you will see any files in that folder when browsing.

If you want completely disable directory listing on cpanel, here the tips:

Login to your server using SSH as root, then edit file /etc/httpd/conf/access.conf :

# pico -w /etc/httpd/conf/access.conf

Change the content so look like this:

<Directory />

Options -Indexes FollowSymLinks ExecCGI Includes
AllowOverride All

order allow,deny
allow from all

</Directory>

Basically it’s change from Indexes to -Indexes
Good luck!