Buffer overflow

In computers and computer security, a buffer overflow occurs when more data is written to a memory buffer than can fit into the memory buffer. In certain programs, the excess data is written to memory beyond that buffer, overwriting other data. This error is the most common type of Computer security flaw, and its prevalence is due to the common use of languages such as C which have no implicit method to prevent buffer overflows.

Other names for this attack include "buffer overrun" and "Smashing the Stack," both of which describe the concept.

Technical Explanation

A software execution stack exists for every process running on a computer. Parts of the stack contain program variables, and other parts contain information such as saved program counter address. Many programs---often because of the nature of the language in which they were written---do not take adequate steps to ensure they cannot overwrite their stacks as a result of invalid inputs. As a result, it is possible to coerce such programs to overwrite their stacks with chosen data.

By overwriting saved program counter addresses, an attacker may modify variables within the program, or even redirect execution to other code, potentially code that the attacker placed onto stack.

This can achieve unexpected results, ranging anywhere from the program crashing, to hijacking the execution context (and therefore, the security context) of the program in question. This simple concept has had profound implications in the annals of computer security.

Related Topics

• Stack frame, which describes the memory management strategy that makes this attack possible

External Links

"Smashing the Stack for Fun and Profit" This article is a bit dated, but it covers in great technical detail this flaw