Need

Prevention of unauthorized access to files and functionalities

Context

• Usage of Dart 2.0 for developing high-performance, cross-platform applications
• Usage of Shelf for managing and organizing data in Node.js applications
• Usage of shelf_router for routing and handling HTTP requests in a Shelf application

Description

Non compliant code

        import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf_router/shelf_router.dart';

class UserController {
  Router _router;

  UserController() {
    _router = Router();
    _router.post('/update', _updateUserData);
  }

  shelf.Response _updateUserData(shelf.Request request) {
    var userId = request.headers['user-id'];
    var updateData = request.readAsString();

    // This is where the vulnerability lies. The application directly uses the user input
    // without any validation or sanitization. Malicious user can inject harmful characters
    // to manipulate the application behaviour and gain unauthorized access to files.
    var result = updateUser(userId, updateData);

    return shelf.Response.ok(result);
  }

  // This is a dummy function representing the update operation
  String updateUser(String userId, String data) {
    // update operation
    return 'User updated successfully';
  }

  Router get router => _router;
}
        
        

In the above code, the _updateUserData method in the UserController class is vulnerable. This method is responsible for updating user data and is exposed as a POST endpoint at /update.

The vulnerability lies in the fact that the method directly uses user-provided data without any validation or sanitization. The user data is read from the request and passed directly to the updateUser method.

This opens up a potential attack vector where a malicious user can inject harmful characters or scripts into the user data. Since the application does not validate or sanitize the user input, it processes the harmful input as is. This can lead to inappropriate behavior in the application, such as unauthorized access to files.

In the worst-case scenario, this vulnerability could be exploited to gain unauthorized access to SharePoint and other functionalities, leading to a potential data breach. Therefore, it is critical to fix this vulnerability by adding appropriate input validation and sanitization.

Steps

• Implement input validation: Before using the user input, validate it against a set of rules. For instance, check if the user ID is in the expected format and does not contain any special characters.
• Sanitize the input: Even after validation, sanitize the input to remove any potentially harmful characters. This will prevent any code injection attacks.
• Use parameterized queries or prepared statements: This will ensure that the user input is always treated as a literal value and not part of the SQL command.
• Implement proper error handling: Do not reveal any system information in error messages that could help an attacker understand the system architecture.
• Use least privilege principle: Limit the permissions of the application to only what is necessary for its functionality. This will minimize the potential damage in case of a security breach.
• Implement access controls: Ensure that only authorized users can access certain functionalities and files.

Compliant code

        import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf_router/shelf_router.dart';

class UserController {
  Router _router;

  UserController() {
    _router = Router();
    _router.post('/update', _updateUserData);
  }

  shelf.Response _updateUserData(shelf.Request request) {
    var userId = request.headers['user-id'];
    var updateData = request.readAsString();

    // Validate the user input
    if (!isValid(userId, updateData)) {
      return shelf.Response.forbidden('Invalid user data');
    }

    // Sanitize the user input
    var sanitizedUserId = sanitize(userId);
    var sanitizedUpdateData = sanitize(updateData);

    // Use parameterized query to update user data
    var result = updateUser(sanitizedUserId, sanitizedUpdateData);

    return shelf.Response.ok(result);
  }

  // This is a dummy function representing the update operation
  String updateUser(String userId, String data) {
    // update operation
    return 'User updated successfully';
  }

  // Validate the user input
  bool isValid(String userId, String data) {
    // Implement validation logic
    return true;
  }

  // Sanitize the user input
  String sanitize(String input) {
    // Implement sanitization logic
    return input;
  }

  Router get router => _router;
}
        
        

The updated code now includes input validation and sanitization to prevent unauthorized access to files.

The isValid function is used to validate the user input. It checks if the user ID and update data are in the expected format and do not contain any special characters. If the validation fails, the function returns a 403 Forbidden response.

The sanitize function is used to sanitize the user input. It removes any potentially harmful characters from the user input. This prevents any code injection attacks.

The updateUser function now uses a parameterized query to update the user data. This ensures that the user input is always treated as a literal value and not part of the SQL command.

The application now follows the principle of least privilege. It only has the necessary permissions for its functionality. This minimizes the potential damage in case of a security breach.

The application also implements access controls to ensure that only authorized users can access certain functionalities and files. This prevents unauthorized access to files.

References

• 201. Unauthorized access to files