HTTP Parameter Pollution

Summary

HTTP Parameter Pollution (HPP) attacks consist of injecting encoded query string delimiters into other existing parameters. If a web application does not properly sanitize the user input, a malicious user can compromise the logic of the application to perform either client-side or server-side attacks. One consequence of HPP attacks is that the attacker can potentially override existing hard-coded HTTP parameters to modify the behavior of an application, bypass input validation checkpoints, and access and possibly exploit variables that may be out of direct reach.