Buffer overflows are a leading type of security vulnerability. In order to understand how a hacker can use a buffer overflow to infiltrate or crash a computer, you need to understand exactly what a buffer is.
This section provides a basic introduction to buffers; experienced users should skip ahead to Section 5.3.
A computer program consists of code that accesses variables stored in various locations in memory. As a program is executed, each variable is assigned a specific amount of memory, determined by the type of information the variable is expected to hold. For example, a Short Integer only needs a little bit of memory, whereas a Long Integer needs more space in the computer's memory (RAM). There are many different possible types of variables, each with its own predefined memory length. The space set aside in the memory is used to store information that the program needs for its execution. The program stores the value of a variable in this memory space, then pulls the value back out of memory when it's needed. This virtual space is called a buffer.
A good analogy for a buffer is a categorized CD collection. You have probably seen the tall CD towers that hold about 300 CDs. Your computer's memory is similar to a CD holder. The difference is that a computer can have millions of slots that are used to store information, compared to the relatively limited space on a CD rack. Our example CD collection consists of three main categories: Oldies, Classical, and ...