There are a lot of potential exploits out there. There are too many to list in a single forum post. There is an entire section of the forum dedicated to the topic. Look in "Hosting Security and Technology".
There are obvious first steps, like using CloudLinux with CageFS and installing ConfigServer Firewall. Use FastCGI or suPHP instead of DSO mode for PHP. Make sure you use extremely long, random passwords. Make sure cpHulk is enabled (assuming you are using cPanel).