Page 654 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Input and Parameter Checking

One of the most notorious security violations is a buffer overflow. This
violation occurs when programmers fail to validate input data

sufficiently, particularly when they do not impose a limit on the
amount of data their software will accept as input. Because such data
is usually stored in an input buffer, when the normal maximum size of
the buffer is exceeded, the extra data is called overflow. Thus, the type
of attack that results when someone attempts to supply malicious

instructions or code as part of program input is called a buffer
overflow. Unfortunately, in many systems such overflow data is often
executed directly by the system under attack at a high level of privilege
or at whatever level of privilege attaches to the process accepting such
input. For nearly all types of operating systems, including Windows,
Unix, Linux, and others, buffer overflows expose some of the most
glaring and profound opportunities for compromise and attack of any
kind of known security vulnerability.

The party responsible for a buffer overflow vulnerability is always the
programmer whose code allowed nonsanitized or unsanitized input.
Due diligence from programmers can eradicate buffer overflows
completely, but only if programmers check all input and parameters
before storing them in any data structure (and limit how much data
can be proffered as input). Proper data validation is the only way to do

away with buffer overflows. Otherwise, discovery of buffer overflows
leads to a familiar pattern of critical security updates that must be
applied to affected systems to close the point of attack.

Maintenance Hooks and Privileged Programs

Maintenance hooks are entry points into a system that are known only
by the developer of the system. Such entry points are also called back
doors. Although the existence of maintenance hooks is a clear
violation of security policy, they still pop up in many systems. The

original purpose of back doors was to provide guaranteed access to the
system for maintenance reasons or if regular access was inadvertently
disabled. The problem is that this type of access bypasses all security
controls and provides free access to anyone who knows that the back
doors exist. It is imperative that you explicitly prohibit such entry