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Lack of data validation - Special Characters

Need​

Implementation of robust data validation for special characters

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 submitButtonTapped(_ sender: Any) {
        let input = textField.text
        processInput(input: input)
    }

    func processInput(input: String?) {
        // Process the input without any validation
    }
}

The above Swift code represents a simple ViewController in an iOS application. It has a single UITextField for user input and a button for submission. When the button is clicked, the submitButtonTapped method is called, which retrieves the text from the UITextField and passes it to the processInput method.

The vulnerability lies in the processInput method. Here, the user's input is processed without any form of validation. This means that if a user enters special characters in the UITextField, the application will process these characters without any checks.

This lack of data validation can lead to various issues depending on how the input is used. For example, if the input is used in a SQL query, it can lead to SQL injection attacks. If the input is displayed back to the user, it can lead to Cross-Site Scripting (XSS) attacks. Even if the input is simply stored and retrieved later, special characters can cause issues with the encoding and decoding of the data.

Therefore, it is crucial to validate user input and sanitize it as necessary to prevent such vulnerabilities.

Steps​

  • Implement data validation for the input field.
  • Define a set of allowed characters and check if the input contains any special characters.
  • Use regular expressions or character comparison to validate the input.
  • Display an error message or prevent the submission if special characters are found.
  • Consider using a library or built-in functions for data validation to ensure accuracy and efficiency.

Compliant code​

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var textField: UITextField!

    @IBAction func submitButtonTapped(_ sender: Any) {
        let input = textField.text
        if validateInput(input: input) {
            processInput(input: input)
        } else {
            // Display an error message
            print("Invalid input. Please avoid using special characters.")
        }
    }

    func processInput(input: String?) {
        // Process the input
    }

    func validateInput(input: String?) -> Bool {
        guard let input = input else { return false }
        let allowedCharacters = CharacterSet.alphanumerics
        let inputCharacters = CharacterSet(charactersIn: input)
        return allowedCharacters.isSuperset(of: inputCharacters)
    }
}

The updated code includes a new function validateInput(input: String?) -> Bool that validates the input from the text field. This function uses the CharacterSet class to define a set of allowed characters (in this case, alphanumeric characters). It then creates a CharacterSet from the input string and checks if the allowed characters set is a superset of the input characters set. If it is, that means the input only contains allowed characters and the function returns true. If not, the function returns false.

In the submitButtonTapped(_ sender: Any) function, the input is now validated before being processed. If the validateInput(input: String?) -> Bool function returns false, an error message is printed to the console and the input is not processed. This prevents any special characters from being processed.

This solution ensures that only valid data is processed by the application, effectively mitigating the risk of injection attacks or other forms of malicious input.

References​

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