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Lack of data validation - Host Header Injection

Need​

Implementation of strict input validation and sanitization for the host header field

Context​

  • Usage of PHP for server-side web development
  • Usage of Request for making HTTP requests

Description​

Non compliant code​

public function redirect(Request $request)
{
    $url = $request->header('Host');
    return redirect($url);
}

The above code is a simple function in a Laravel controller that redirects the user to a URL specified in the Host header of an incoming request.

This code is vulnerable to Host Header Injection attacks because it doesn't validate the Host header from the request before using it. This means an attacker can manipulate the Host header to make the application redirect the user to a malicious website.

In a Host Header Injection attack, the attacker sends a request with a manipulated Host header that contains the URL of a malicious website. The application then uses this URL to generate a redirect response, leading the user to the attacker's site.

This can lead to various threats like phishing, where the attacker tricks the user into revealing sensitive information (e.g., passwords, credit card numbers), or malware distribution, where the attacker's site automatically downloads malicious software onto the user's device.

The lack of data validation makes this code vulnerable. It's generally a bad practice to trust user input (including HTTP headers) without validation. This code should be fixed by adding validation logic to ensure the Host header contains a safe URL before using it for redirection.

Steps​

  • Validate the 'Host' header to ensure it only contains expected values.
  • Implement a whitelist of allowed hosts and check if the 'Host' header is in this list before redirecting.
  • If the 'Host' header is not in the whitelist, redirect to a default or error page.
  • Consider using a framework or library that provides built-in protection against Host Header Injection.

Compliant code​

public function redirect(Request $request)
{
    $allowed_hosts = ['www.example.com', 'example.com']; // Add your allowed hosts here
    $host = $request->header('Host');

    if (!in_array($host, $allowed_hosts)) {
        // If the host is not in the whitelist, redirect to a default or error page
        return redirect('error_page');
    }

    return redirect($host);
}

The above code fixes the Host Header Injection vulnerability by implementing a whitelist of allowed hosts. The $allowed_hosts array contains the list of allowed hosts. When a request is made, the 'Host' header is retrieved from the request and checked against the whitelist.

If the 'Host' header is not in the whitelist, the function redirects to a default error page. This prevents the application from redirecting to a potentially malicious website if the 'Host' header is manipulated.

This solution effectively mitigates the risk of Host Header Injection by ensuring that only valid and trusted hosts are allowed. It is also recommended to use a framework or library that provides built-in protection against such vulnerabilities. Laravel, the framework being used in this context, has several security features that can be utilized to further enhance the security of the application.

References​

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