Book Image

The Web Application Hacker's Handbook

By : Dafydd Stuttard, Marcus Pinto
Book Image

The Web Application Hacker's Handbook

By: Dafydd Stuttard, Marcus Pinto

Overview of this book

Web applications are the front door to most organizations, exposing them to attacks that may disclose personal information, execute fraudulent transactions, or compromise ordinary users. This practical book has been completely updated and revised to discuss the latest step-by-step techniques for attacking and defending the range of ever-evolving web applications. Youíll explore the various new technologies employed in web applications that have appeared since the first edition and review the new attack techniques that have been developed, particularly in relation to the client side. The book starts with the current state of web application security and the trends that indicate how it is likely to evolve soon. Youíll examine the core security problem affecting web applications and the defence mechanisms that applications implement to address this problem, and youíll also explore the key technologies used in todayís web application. Next, youíll carry out tasks for breaking into web applications and for executing a comprehensive attack. As you progress, youíll learn to find vulnerabilities in an application's source code and review the tools that can help when you hack web applications. Youíll also study a detailed methodology for performing a comprehensive and deep attack against a specific target. By the end of this book, youíll be able to discover security flaws in web applications and how to deal with them.
Table of Contents (32 chapters)
Free Chapter
About the Authors
About the Technical Editor
MDSec: The Authors’ Company
End User License Agreement

Format String Vulnerabilities

Format string vulnerabilities arise when user-controllable input is passed as the format string parameter to a function that takes format specifiers that may be misused, as in the printf family of functions in C. These functions take a variable number of parameters, which may consist of different data types such as numbers and strings. The format string passed to the function contains specifiers, which tell it what kind of data is contained in the variable parameters, and in what format it should be rendered.

For example, the following code outputs a message containing the value of the count variable, rendered as a decimal:

printf("The value of count is %d", count.);

The most dangerous format specifier is %n. This does not cause any data to be printed. Rather, it causes the number of bytes output so far to be written to the address of the pointer passed in as the associated variable parameter. For example:

int count = 43;
int written = 0;