HTTP parameter pollution
HTTP Parameter Pollution (HPP) is a web application vulnerability exploited by injecting encoded query string delimiters in already existing parameters. The vulnerability occurs if user input is not correctly encoded for output by a web application.[1] This vulnerability allows the injection of parameters into web application-created URLs. It was first brought forth to the public in 2009 by Stefano di Paola and Luca Carettoni, in the conference OWASP EU09 Poland.[1] The impact of such vulnerability varies, and it can range from "simple annoyance" to complete disruption of the intended behavior of a web application. Overriding HTTP parameters to alter a web application's behavior, bypassing input and access validation checkpoints, as well as other indirect vulnerabilities, are possible consequences of a HPP attack.[1]
| HTTP |
|---|
 |
| Request methods |
| Header fields |
| Response status codes |
| Security access control methods |
| Security vulnerabilities |
There is no RFC standard on what should be done when it has passed multiple parameters. HPP could be used for cross channel pollution, bypassing CSRF protection and WAF input validation checks.[2]
Behaviour
When they are passed multiple parameters with the same name, here is how various back ends behave.[3]
| Technology | Parsing result | Example |
|---|---|---|
| ASP.NET/IIS | All occurrences concatenated with a comma | param=val1,val2 |
| ASP/IIS | All occurrences concatenated with a comma | param=val1,val2 |
| PHP/Apache | Last occurrence only | param=val2 |
| PHP/Zeus | Last occurrence only | param=val2 |
| JSP, Servlet/Apache Tomcat | First occurrence only | param=val1 |
| JSP, Servlet/Oracle Application Server | First occurrence only | param=val1 |
| JSP, Servlet/Jetty | First occurrence only | param=val1 |
| IBM Lotus Domino | Last occurrence only | param=val2 |
| IBM HTTP Server | First occurrence only | param=val1 |
| mod_perl,libapreq2/Apache | First occurrence only | param=val1 |
| Perl CGI/Apache | First occurrence only | param=val1 |
| mod_wsgi (Python)/Apache | First occurrence only | param=val1 |
| Python/Zope | All occurrences in list(array) | param=['val1','val2'] |
Types
Prevention
Proper input validation and awareness about web technology on HPP is protection against HTTP Parameter Pollution.[5]
References
- Balduzzi et al. 2011, p. 2.
- "HTTP Parameter Pollution Vulnerabilities in Web Applications" (PDF). 2011.
- "WSTG - Latest:Testing for HTTP Parameter Pollution".
- Luca Carettoni; Stefano Di Paola. "HTTP Parameter Pollution" (PDF).
- "How to Detect HTTP Parameter Pollution Attacks".
Bibliography
- Balduzzi, Marco; Torrano-Gimenez, Carmen; Balzarotti, Davide; Kirda, Engin (2011). Automated Discovery of Parameter Pollution Vulnerabilities in Web Applications. Proceedings of the Network and Distributed System Security Symposium, NDSS 2011 – via ResearchGate.