Online compilers are a handy tool to save time and resources for coders, and are freely available for a variety of programming languages. They are useful for learning a new language and developing simple programs, such as the ubiquitous “Hello World” exercise. I often use online compilers when I am out, so that I don’t have to worry about locating and downloading all of the resources myself. Since these online tools are essentially remote compilers with a web interface, I realized that I might be able to take remote control of the machines through command injection. My research identified a common weakness in many compilers: inadequate sanitization of user-submitted code prior to execution. My analysis revealed that this lack of input filtration enables exploits that an hacker can use to take control of the machine or deliberately cause it to crash. A clever attacker can exploit built-in C functions and POSIX libraries to gain control over the computer hosti...