Network trace analysis provides a terrific insight into the working of a web application. Identifying the output data from the application to the browser is relatively straightforward, but there are many different ways that the browser can send data to the application.
Hidden data carried in packets destined for the web server can influence load balancers, firewalls and proxies as well as enabling the web site to maintain context information (login status, basket contents, etc.).
In this video we identify 5 common hiding places for this data using Wireshark and Network Monitor traces.