Skip to main content

Authentication mechanism absence or evasion - Redirect

Need​

Implementation of a robust and secure authentication mechanism

Context​

  • Usage of Swift for iOS and macOS app development
  • Usage of UIKit for building modern and responsive user interfaces
  • Usage of Alamofire for making network requests in iOS development

Description​

Non compliant code​

import UIKit
import Alamofire

class LoginViewController: UIViewController {
    @IBOutlet weak var usernameField: UITextField!
    
    @IBAction func loginButtonTapped(_ sender: Any) {
        let username = usernameField.text!
        
        let parameters: Parameters = ["username": username]
        
        Alamofire.request("http://example.com/login", method: .post, parameters: parameters, encoding: JSONEncoding.default).responseJSON { response in
            if let jsonResponse = response.result.value as? [String: Any] {
                if let redirect = jsonResponse["redirect"] as? String {
                    let viewController = self.storyboard?.instantiateViewController(withIdentifier: redirect)
                    self.present(viewController!, animated: true, completion: nil)
                }
            }
        }
    }
}

The above Swift code is for a login view controller in an iOS application. The user enters a username and taps the login button, triggering the loginButtonTapped function.

This function sends a POST request to the server, which is supposed to authenticate the user. The server then responds with a JSON object that includes a "redirect" field. This field tells the app which view controller to present next.

The vulnerability lies in the fact that the server's response is trusted implicitly. There is no authentication mechanism in place to ensure that the server's response is valid and safe.

Therefore, an attacker could intercept the server's response and modify the "redirect" field. This could cause the app to present a view controller that the attacker wants, potentially leading to unauthorized access to sensitive parts of the app.

For example, if the app has a view controller with the identifier "AdminViewController", an attacker could potentially gain access to this view controller by changing the "redirect" field in the server's response.

This vulnerability is a type of Authentication mechanism absence or evasion, specifically a Redirect vulnerability.

Steps​

  • Implement a secure authentication mechanism such as username/password validation or token-based authentication.
  • Ensure that the server-side code validates the username and password before granting access to the application.
  • Do not rely solely on client-side validation for authentication.
  • Avoid using redirects as a means of authentication. Instead, use a secure session management approach.
  • Implement server-side checks to prevent unauthorized access to sensitive resources.
  • Regularly update and patch the server-side code to address any security vulnerabilities.

Compliant code​

import UIKit
import Alamofire

class LoginViewController: UIViewController {
    @IBOutlet weak var usernameField: UITextField!
    @IBOutlet weak var passwordField: UITextField!
    
    @IBAction func loginButtonTapped(_ sender: Any) {
        let username = usernameField.text!
        let password = passwordField.text!
        
        let parameters: Parameters = ["username": username, "password": password]
        
        Alamofire.request("http://example.com/login", method: .post, parameters: parameters, encoding: JSONEncoding.default).responseJSON { response in
            if let jsonResponse = response.result.value as? [String: Any] {
                if let success = jsonResponse["success"] as? Bool {
                    if success {
                        let viewController = self.storyboard?.instantiateViewController(withIdentifier: "HomeViewController")
                        self.present(viewController!, animated: true, completion: nil)
                    } else {
                        // Handle login failure
                    }
                }
            }
        }
    }
}

The updated code now includes a password field, and the parameters sent to the server include both the username and password. This is a basic form of authentication that can help prevent unauthorized access.

The server-side code should validate the username and password before sending a response. If the validation is successful, the server should return a JSON response with a "success" key set to true. If the validation fails, the "success" key should be set to false.

The client-side code checks the value of the "success" key in the server's response. If the login is successful, the user is redirected to the home view controller. If the login fails, the failure is handled appropriately (this could involve showing an error message to the user, for example).

This approach avoids using redirects as a means of authentication, which can be insecure. Instead, it uses a secure session management approach, where the server maintains the state of the user's session and only allows access to resources if the user is authenticated.

Remember to regularly update and patch the server-side code to address any security vulnerabilities.

References​

Last updated on