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HTTP parameter pollution

Need​

Prevention of HTTP parameter pollution

Context​

  • Usage of PHP 7.0+ for server-side scripting and web development
  • Usage of Request for making HTTP requests
  • Usage of the User dependency for user-related functionality

Description​

Non compliant code​

public function index(Request $request)
{
    $id = $request->input('id');
    $user = User::find($id);

    return view('user.profile', ['user' => $user]);
}

The above PHP code is an example of a HTTP Parameter Pollution (HPP) vulnerability. This is a common issue in web applications where the application allows extra parameters injection to HTTP communication protocol.

In the code, we are taking a user input directly from the HTTP request and using it to query the database without any form of validation or sanitization. This can lead to unexpected behavior if a malicious user decides to manipulate the 'id' parameter in the HTTP request.

For example, a malicious user can send a request like 'GET /user?id=1&id=2'. The Laravel framework will only consider the last 'id' parameter, so it will return the profile of user with id=2. However, other frameworks or languages might consider both parameters and this can cause unexpected behavior.

This vulnerability can be exploited in different ways, such as data leakage, data loss, or even remote code execution depending on the context. It is therefore crucial to always validate and sanitize user inputs before using them in any form of data processing or database querying to prevent such vulnerabilities.

Steps​

  • Validate the input parameters to ensure they are as expected. This can be done using Laravel's validation rules.
  • Sanitize the input parameters to remove any unwanted characters or strings. Laravel provides several methods for this.
  • Use prepared statements or parameterized queries when interacting with the database to prevent SQL injection attacks.
  • Implement a strong error handling mechanism to prevent the disclosure of sensitive information in case of an error.
  • Regularly update and patch the application and its dependencies to protect against known vulnerabilities.

Compliant code​

public function index(Request $request)
{
    $validatedData = $request->validate([
        'id' => 'required|integer',
    ]);

    $id = $validatedData['id'];
    $user = User::find($id);

    if (!$user) {
        abort(404, 'User not found');
    }

    return view('user.profile', ['user' => $user]);
}

The updated code now includes input validation to ensure that the 'id' parameter is present and is an integer. This is done using Laravel's built-in validation rules. The 'validate' method automatically handles returning a response if the validation fails.

The 'id' is then retrieved from the validated data, rather than directly from the request. This ensures that only the validated and sanitized data is used.

When retrieving the user from the database, we now check if the user exists. If not, we return a 404 error. This prevents the application from breaking if an invalid 'id' is provided and improves the error handling of the application.

This code fixes the HTTP parameter pollution vulnerability by ensuring that only valid and expected parameters are used. It also improves the error handling of the application and prevents potential SQL injection attacks by using Laravel's Eloquent ORM for database interactions.

References​

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