Identification of HTTP Response Splitting

HTTP response splitting is a web vulnerability that occurs when an application fails to properly sanitize user input that is included in HTTP headers. Attackers can exploit this vulnerability to manipulate server responses, adding arbitrary headers or controlling the body of the response. This can lead to various attacks, such as cache poisoning, cross-site scripting (XSS), and website defacement.

Common Indicators of HTTP Response Splitting:

  1. User-Controlled Input in Headers: If the application includes user-controlled input in HTTP response headers without proper sanitization, it might be vulnerable to HTTP response splitting.
  2. Carriage Return and Line Feed (CRLF) Injection: The presence of user input that includes carriage return (CR, \r) and line feed (LF, \n) characters can lead to HTTP response splitting, as these characters can be used to split the response.
  3. Unexpected Redirects and Content: Observing unexpected redirects, additional HTTP headers, or unexpected content in the response can be indicative of HTTP response splitting.

How to Identify HTTP Response Splitting:

  1. Manual Testing: Manipulate HTTP requests by injecting CRLF characters followed by arbitrary headers or content into user-controllable input fields. If the server's response reflects these injections, it indicates vulnerability.
  2. Automated Scanning Tools: Use web security scanners that can identify HTTP response splitting vulnerabilities by testing various injection payloads.
  3. Code Review: Analyze the application's source code for instances where user input is included in HTTP response headers. Look for lack of or improper sanitization of CRLF characters.
  4. Penetration Testing: Conduct penetration testing with a focus on manipulating HTTP headers and observing the application's response, looking for indications of successful response splitting.

Mitigation Strategies:

  1. Input Validation: Ensure rigorous validation of all user-supplied input, especially data that is included in HTTP headers. Specifically, sanitize input to remove or encode CRLF characters.
  2. Use Proper Encoding: Apply proper encoding or escaping to user-controlled input to ensure that special characters, such as CR and LF, do not have their native meanings interpreted by the server.
  3. Library Functions: Utilize library functions and frameworks that inherently encode or sanitize output, reducing the risk of header injection and response splitting.
  4. Security Headers: Implement security headers that can help mitigate the impact of response splitting, such as Content Security Policy (CSP).
  5. Regular Auditing: Regularly audit and test the application for injection vulnerabilities, including HTTP response splitting, to ensure that new code or changes to the application do not introduce vulnerabilities.

Addressing HTTP response splitting is crucial for securing web applications, as this vulnerability can compromise the integrity of web communications and lead to a range of web-based attacks.