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Lack of data validation - Input Length

Need​

Implementation of input length validation

Context​

  • Usage of Swift for iOS and macOS app development
  • Usage of UIKit for building modern and responsive user interfaces

Description​

Non compliant code​

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var textField: UITextField!
    
    @IBAction func submitButtonPressed(_ sender: UIButton) {
        let inputText = textField.text
        processData(input: inputText)
    }
    
    func processData(input: String?) {
        // Some processing code here
    }
}

The above Swift code represents a typical scenario in a mobile application where a text field input is taken from the user and processed without any validation of the input length.

Here, in the submitButtonPressed(_:) function, the text from the textField is directly taken and passed to the processData(input:) function without any check on the length of the input. This can allow an attacker to send massive amounts of characters and potentially crash the application or exploit other vulnerabilities.

The vulnerability lies in the lack of input length validation. The application does not limit the number of characters that can be entered into the text field, thus opening up the possibility for Buffer Overflow attacks. This can lead to unexpected behavior, including the application crashing or more serious security risks like code execution or memory corruption.

To mitigate this vulnerability, the application should enforce a maximum length for the input field, either on the client side (i.e., in the mobile app itself), the server side, or both. This can be done by checking the length of the input text before processing it.

Steps​

  • Implement input length validation on the server-side to restrict the maximum allowed input length.
  • Add client-side input length validation to limit the input length before sending it to the server.
  • Use appropriate data types and length constraints for the input parameters in the server-side processing code.
  • Consider implementing rate limiting or throttling mechanisms to prevent abuse of the endpoint by sending massive amounts of data.
  • Regularly update and patch the server-side code to address any potential security vulnerabilities.

Compliant code​

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var textField: UITextField!
    
    @IBAction func submitButtonPressed(_ sender: UIButton) {
        guard let inputText = textField.text else { return }
        if inputText.count <= 500 {
            processData(input: inputText)
        } else {
            // Show an error message to the user
            print("Input is too long")
        }
    }
    
    func processData(input: String) {
        // Some processing code here
    }
}

The updated code now includes a check for the length of the input text before it is processed. If the length of the input text is greater than 500 characters, the function will not process the data and instead print an error message. This is a simple form of client-side validation that can help prevent the server from receiving and processing overly long inputs.

However, it's important to note that client-side validation can be bypassed, so it's crucial to also implement server-side validation. The server-side code should also check the length of the input and reject any inputs that are too long.

In addition to input length validation, consider implementing rate limiting or throttling mechanisms on the server to prevent abuse of the endpoint by sending massive amounts of data. Regularly updating and patching the server-side code can also help address any potential security vulnerabilities.

References​

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