Buffer overflows are a leading type of security vulnerability. This paper explains what a buffer overflow is, how it can be exploited, and what countermeasures can be taken to prevent the use of buffer overflow vulnerabilities.

Buffer overflow vulnerabilities are one of the most common vulnerabilities. These kinds of vulnerabilities are perfect for remote access attacks because they give the attacker a great opportunity to launch and execute their attack code on the target computer. Broadly speaking, a buffer overflow attack occurs when the attacker intentionally enters more data than a program was written to handle. The data runs over and overflows the section of memory that was set aside to accept it. The extra data overwrites on top on another portion of memory that was meant to hold something else, like part of the program's instructions. This allows an attacker to overwrite data that controls the program and can takeover control of the program to execute the attacker's code instead of the program. Peikari and Chuvakin point out that, "buffer overflows result from an inherent weakness in the C++ programming language." (Peikari and Chuvakin, 2004) The problem is that C++ and other programming languages (those derived from C++), do not automatically perform bounds-checking when passing data. When variables are passed, extra characters could be written past the variable's end. The overflow consequence could result in the program crashing or allowing the attacker to execute their own code on the target system.

In order to make sense of how a buffer is overflowed, one must understand what a buffer is. A program contains code that accesses variables stored in various locations in memory. When a program is executed, a specific amount of memory is assigned for each variable. The amount of memory is determined by the type of data the variable is anticipated to hold. The memory set aside is used to store information that the program needs for its execution. According to Peikari and Chuvakin , "The program stores the value of a variable in this memory space, then pulls the value back out of memory when it's needed." (Peikari and Chuvakin, 2004) A buffer is this virtual space.

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