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
1
Cover
2
Title
3
Copyright
4
About the Authors
5
About the Technical Editor
6
MDSec: The Authors’ Company
7
Credits
8
Acknowledgments
31
Index
32
End User License Agreement

Integer Vulnerabilities

Integer-related vulnerabilities typically arise when an application performs some arithmetic on a length value before performing some buffer operation but fails to take into account certain features of how compilers and processors handle integers. Two types of integer bugs are worthy of note: overflows and signedness errors.

Integer Overflows

These occur when an operation on an integer value causes it to increase above its maximum possible value or decrease below its minimum possible value. When this occurs, the number wraps, so a very large number becomes very small, or vice versa.

Consider the following “fix” to the heap overflow described previously:


bool CheckLogin(char* username, char* password)
{
    unsigned short len = strlen(username) + 1;
    char* _username = (char*) malloc(len);
    strcpy(_username, username);
    ...

Here, the application measures the length of the user-submitted username, adds 1 to accommodate the trailing null,...