HTTP Parameter Pollution
Summary
HTTP Parameter Pollution (HPP) is a Web attack evasion technique that allows an attacker to craft a HTTP request in order to manipulate web logics or retrieve hidden information. This evasion technique is based on splitting an attack vector between multiple instances of a parameter with the same name (?param1=value¶m1=value). As there is no formal way of parsing HTTP parameters, individual web technologies have their own unique way of parsing and reading URL parameters with the same name. Some taking the first occurance, some taking the last occurance, and some reading it as an array. This behavior is abused by the attacker in order to bypass pattern-based security mechanisms.
Tools
No tools needed. Maybe Burp or OWASP ZAP.
How to test
HPP allows an attacker to bypass pattern based/black list proxies or Web Application Firewall detection mechanisms. This can be done with or without the knowledge of the web technology behind the proxy, and can be achieved through simple trial and error.
Table of refence for which technology reads which parameter
When ?par1=a&par1=b
References
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