Data that is not validated or poorly validated is the root cause of a number of serious security vulnerabilities affecting applications. This paper presents a modular approach to performing through data validation in modern web applications so that the benefits of modular component based design; extensibility, portability and re-use can be released. The paper begins with an explanation of the vulnerabilities introduced through poor validation and then goes on to discuss the merits of a number of common data validation methodologies. A modular approach is introduced together with practical examples of how to implement such a scheme in a web application. It also provides information on common attack vectors, principles of validation, a modular solution and implementation of that solution.
