All websites in this day and age provide dynamic responses to users that are informed by some external database or inferred from a process external to the HTML itself. On the clients, this is typically cordoned off and restricted to the Domain Object Model (DOM) space of the browser, but on the servers the variety and scope of these intertwined processes become exceedingly hard to manage. With all of a typical enterprise's defences tuned to permit application-bound traffic into the web tier, and the web tier, in turn, trusted to access the application and database tiers, hackers have learned to web tier into their stooge. The web tier unwittingly becomes an insider threat, and with it comes all privileged access and trust relationships.
Injections are a powerful and common form of compromising the client-server connection and can be used to...