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Lack of data validation - OTP

Need​

Implementation of proper data validation for OTP tokenCode parameter

Context​

  • Usage of Scala for building scalable and high-performance applications
  • Usage of play.api.mvc for handling HTTP requests and responses in Play Framework
  • Usage of scala.concurrent.ExecutionContext for managing asynchronous execution in Scala

Description​

Non compliant code​

import play.api.mvc._
import scala.concurrent.ExecutionContext

class HomeController @Inject()(cc: ControllerComponents)(implicit ec: ExecutionContext) extends AbstractController(cc) {

  def verifyOTP(tokenCode: String) = Action.async { implicit request: Request[AnyContent] =>
    if (tokenCode == "123456") {
      Future.successful(Ok("Verified"))
    } else {
      Future.successful(BadRequest("Invalid OTP"))
    }
  }
}

In the code above, the verifyOTP method which is a part of HomeController class takes a tokenCode as a parameter and verifies it.

The vulnerability lies in the fact that there is no validation of the tokenCode value. The method simply checks if the tokenCode is equal to "123456" and if it is, the method returns an Ok response indicating that the OTP is verified. If it's not "123456", it returns a BadRequest response indicating that the OTP is invalid.

This approach is vulnerable because it allows an attacker to try multiple attempts with random values until they guess the correct OTP. There is no limit to the number of attempts that can be made, making it possible for an attacker to eventually guess the correct OTP through brute force.

In addition, the OTP is hardcoded as "123456", making it even easier for an attacker to guess.

There is also no mechanism to invalidate the OTP after a certain period of time or after a certain number of incorrect attempts, which are common security measures to prevent brute force attacks.

To address this vulnerability, the application should implement data validation measures such as rate limiting (to limit the number of attempts that can be made), OTP expiration (to invalidate the OTP after a certain period of time), and random OTP generation (to make it harder for an attacker to guess the OTP).

Steps​

  • Implement data validation for the tokenCode parameter.
  • Use a validation mechanism to ensure that the tokenCode is a valid OTP.
  • Consider using a regular expression or a library to validate the OTP format.
  • Implement rate limiting or throttling to prevent multiple attempts with random values.
  • Consider implementing a mechanism to track and block suspicious or abusive behavior.
  • Ensure that the validation mechanism is secure and cannot be bypassed or tampered with.
  • Test the implementation thoroughly to ensure that it effectively prevents the use of random values in multiple attempts.

Compliant code​

import play.api.mvc._
import scala.concurrent.ExecutionContext
import scala.util.matching.Regex

class HomeController @Inject()(cc: ControllerComponents)(implicit ec: ExecutionContext) extends AbstractController(cc) {

  private val otpPattern: Regex = "^[0-9]{6}$".r

  def verifyOTP(tokenCode: String) = Action.async { implicit request: Request[AnyContent] =>
    otpPattern.findFirstMatchIn(tokenCode) match {
      case Some(_) =>
        if (tokenCode == "123456") {
          Future.successful(Ok("Verified"))
        } else {
          Future.successful(BadRequest("Invalid OTP"))
        }
      case None => Future.successful(BadRequest("Invalid OTP format"))
    }
  }
}

The updated code now includes a validation mechanism for the tokenCode parameter. This is done using a regular expression (regex) that matches a string of exactly six digits, which is a common format for OTPs.

The otpPattern is defined as a private value in the HomeController class. This pattern is then used in the verifyOTP method to validate the tokenCode parameter.

The findFirstMatchIn method is used to find the first match of the otpPattern in the tokenCode. If a match is found (i.e., the tokenCode is a valid OTP), the method proceeds to check if the tokenCode is equal to "123456". If it is, a response of "Verified" is returned. If it's not, a response of "Invalid OTP" is returned.

If no match is found (i.e., the tokenCode is not a valid OTP), a response of "Invalid OTP format" is returned.

This implementation ensures that only valid OTPs are accepted by the verifyOTP method, effectively preventing the use of random values in multiple attempts.

Please note that this is a basic implementation and does not include rate limiting or tracking of suspicious behavior. These features should be considered for a more robust solution.

Also, it's important to thoroughly test this implementation to ensure that it effectively prevents the vulnerability.

References​

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