HTTP Parameter Pollution

HTTP Parameter Pollution (HPP) is a type of web application vulnerability that affects the security of the web applications. It occurs when the application takes user-supplied data in the form of URL parameters, and uses them without proper validation. As a result, attackers can manipulate these parameters to inject malicious payloads, leading to various security issues such as Cross-Site Scripting (XSS), SQL Injection, and other attacks.

HPP occurs when the web application allows multiple instances of the same parameter in a single HTTP request. For example, consider the following URL:

In this example, the q parameter is repeated twice, which can lead to unexpected behavior. The web application may use only the first instance of the q parameter, or it may use both instances and combine the results in an unexpected way.

To prevent HPP, developers must ensure that their web applications validate user-supplied input and reject any requests that contain multiple instances of the same parameter. They can also use secure coding practices, such as input validation, output encoding, and parameter-based URL rewriting, to mitigate the risk of HPP attacks.

In addition, web application firewalls (WAFs) can also be used to protect against HPP attacks by detecting and blocking malicious requests. However, it’s important to note that WAFs are not a silver bullet and should be used in conjunction with other security measures, such as proper input validation and output encoding.

In conclusion, HPP is a serious security issue that can lead to various attacks on web applications. Developers and security professionals should take the necessary steps to prevent HPP attacks by implementing secure coding practices and using security measures like WAFs. By doing so, they can help ensure that their web applications are protected from HPP attacks and other security threats.