Chapter 4 described various techniques you can use to map a target application and gain an initial understanding of how it works. That methodology involved interacting with the application in largely benign ways to catalog its content and functionality, determine the technologies in use, and identify the key attack surface.
This chapter describes ways in which you can extract further information from an application during an actual attack. This mainly involves interacting with the application in unexpected and malicious ways and exploiting anomalies in the application's behavior to extract information that is of value to you. If successful, such an attack may enable you to retrieve sensitive data such as user credentials, gain a deeper understanding of an error condition to fine-tune your attack, discover more details about the technologies in use, and map the application's internal structure and functionality.
Exploiting Error Messages
Many web applications return informative error messages when unexpected events occur. These may range from simple built-in messages that disclose only the category of the error to full-blown debugging information that gives away a lot of details about the application's state.
Most applications are subject to various kinds of usability testing prior to deployment. This testing typically identifies most error conditions that may arise when the application is being used in the normal way. Therefore, ...