HTTP Response Splitting

HTTP Response Splitting is a web application security vulnerability that occurs when an attacker manipulates the HTTP response headers of a server by injecting unvalidated user input. This exploitation causes the server to generate multiple HTTP responses instead of a single, expected response. As a result, the attacker can control the behavior of the subsequent HTTP response, potentially leading to various attacks such as web cache poisoning, cross-site scripting (XSS), or unauthorized redirection.

HTTP Response Splitting occurs when an application improperly validates or sanitizes user-supplied input included in HTTP response headers. If the input contains carriage return (\r) and line feed (\n) characters, it can prematurely terminate the intended headers and inject additional, malicious headers or a body in the HTTP response.

Testing for HTTP Response Splitting is critical for ensuring web application security, as this vulnerability can be exploited to compromise both user data and application integrity.

Key Testing Areas:

• Input Validation: Ensure all user inputs included in HTTP headers are thoroughly validated and sanitized.
• Header Injection Detection: Simulate attack scenarios by injecting payloads containing \r and \n to identify improper response handling.
• Dynamic Testing: Use penetration testing tools to evaluate how the application handles crafted HTTP requests.

Prevention and Mitigation

To prevent HTTP Response Splitting, developers and testers should focus on:

1. Properly validating and encoding user inputs to ensure that special characters like \r and \n cannot terminate or inject headers.
2. Avoiding direct embedding of user-supplied data into HTTP response headers without sanitization.
3. Using secure frameworks and libraries that handle HTTP headers safely.
4. Implementing strict Content Security Policies (CSPs) to minimize the impact of potential exploits.