HTTP Parameter Pollution (HPP) is a type of web application vulnerability that occurs when an attacker manipulates HTTP requests by injecting multiple parameters with the same name into the URL or request body. This can lead to unexpected behavior in the application, as the application might not handle multiple parameters with the same name properly, leading to errors or security flaws.
HPP exploits how web servers and applications process HTTP requests. When an attacker sends a request with duplicate parameters (same parameter name with different values), some applications might not handle these properly, allowing attackers to manipulate application behavior. This can occur in both GET and POST requests.
Injecting Multiple Parameters: An attacker includes multiple parameters with the same name in the URL or request body. For example: http://example.com/page?param=value1¶m=value2.
Exploiting Application Logic: Depending on how the application processes these parameters, it might accept one value or process the request incorrectly, potentially causing vulnerabilities such as parameter-based bypasses or SQL injection.
Triggering Unexpected Behavior: If the application does not properly validate or sanitize the parameters, it may cause errors, unauthorized access, bypassing security checks, or data manipulation.
HPP attacks can lead to several severe security risks, particularly when the application fails to properly handle injected parameters:
Bypassing Security Filters: Attackers may exploit HPP to bypass input validation mechanisms, such as authentication checks, input sanitization, or access controls.
Session Fixation and Hijacking: By manipulating session parameters, attackers could hijack user sessions or fixate sessions to impersonate legitimate users.
SQL Injection and Other Attacks: If parameters are improperly processed and used in queries (e.g., SQL queries), HPP can inject malicious SQL code, leading to data leaks or corruption.
Unexpected Application Behavior: Improper handling of parameters might cause errors or crashes, leading to potential denial of service (DoS) attacks or unintentional exposure of sensitive data.
To defend against HPP attacks and prevent associated risks:
Validate and Sanitize Input Parameters: Ensure input parameters are validated and sanitized before processing. This includes preventing duplicate or maliciously crafted parameters.
Reject Duplicate Parameters: Applications should reject requests with multiple parameters of the same name or only accept the first valid parameter.
Use Parameterized Queries: Always use parameterized queries for database interactions to prevent SQL injection, treating parameters as data, not executable code.
Apply Web Application Firewalls (WAFs): A WAF can detect and block suspicious requests with duplicate parameters or malicious payloads, adding security.
Use Secure Frameworks: Frameworks with built-in input validation and sanitization can reduce HPP attack chances by handling HTTP parameters safely.
While preventing HPP attacks is achievable, there are several challenges:
Complexity in Identifying Duplicate Parameters: Not all applications or frameworks handle or detect duplicate parameters easily, requiring custom security measures through thorough code reviews or vulnerability assessments.
Legacy Systems: Older web applications without modern security practices may be more vulnerable. Updating these to handle parameter validation properly might require significant changes.
Balancing Security and Performance: Implementing parameter validation and other security measures may impact performance, especially if requests are heavily filtered for duplicates. Optimizing checks without sacrificing performance is challenging.
User Experience: Proper validation might lead to rejecting legitimate requests if parameters are not handled correctly. Ensuring validation does not negatively impact legitimate user interactions is important.
HTTP Parameter Pollution is a significant vulnerability that exploits how web applications process duplicate parameters in HTTP requests. By leveraging HPP, attackers can bypass security measures, hijack sessions, or inject malicious payloads like SQL queries. Preventing HPP requires robust input validation, proper handling of duplicate parameters, and using secure practices like parameterized queries. By adopting these precautions and conducting regular security assessments, web applications can minimize the risk of HPP attacks and better protect their users.