When we are talking about cybersecurity, the first term comes in mind is hacking. So first investigate how hacking happens. We know our CPU there are multiple registers, and one notable entry is the Program Counter. Processors fetch the next instruction from Program Counter. So if anyhow we can send a byte to the program counter. We hack that computer. All C programmer knows that the process has two major memory components - code segment and data segment. In the code segment, program instructions reside. And data segments takes the external input. So if we flood the code input with a massive amount of data, then data segment overflows, and input byte enters into the code segment. So if a program does not has a proper validation method, providing intelligent input to its the argument, it is possible to control that computer. This is known as the vulnerability of that program. If you go to the Offensive Security portal, you can find many popular applications like MySql has known vulnerability. So a web hacker can scan the ports of a web server, and as a program like Mysql ports and vulnerability both are well-known, they can hack the server. This is a birds-eye view on a web server hacking.