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Authentication mechanism absence or evasion - Response tampering


Implementation of a secure and reliable authentication mechanism


  • Usage of Scala 2.13 for building scalable and high-performance applications
  • Usage of play.api.mvc for handling HTTP requests and responses in Play Framework
  • Usage of play.api.libs.json for JSON parsing and manipulation in Play Framework
  • Usage of for making HTTP requests in Play Framework
  • Usage of for handling HTTP responses in Play Framework


Non compliant code

import play.api.mvc._
import play.api.libs.json._

class OTPController @Inject()(cc: ControllerComponents) extends AbstractController(cc) {

def validateOTP() = Action(parse.json) { request =>
val otp = (request.body \\ "otp").as[String]
val response = WS.url("")
.withQueryString("otp" -> otp)
.map(response => (response.json \\ "success").as[Boolean])

if (response) {
Ok(Json.obj("status" -> "success", "message" -> "OTP validated successfully"))
} else {
BadRequest(Json.obj("status" -> "error", "message" -> "Invalid OTP"))

The above code snippet handles OTP validation in a Play Framework application. When a request is made to the validateOTP endpoint with a JSON body containing the OTP, it makes a request to an external service ( to validate the OTP.

The problem with this code is that it trusts the response from the external service without any further checks. If an attacker can intercept and modify the response from the OTP validation service to always include "success": true, they can bypass the OTP validation and gain unauthorized access.

This is a classic example of a man-in-the-middle attack where the attacker intercepts and tampers with the communication between two parties. In this case, the two parties are our application and the OTP validation service. The attacker can alter the response from the OTP validation service to trick our application into thinking that the OTP is valid, even when it's not.

This is a serious security vulnerability as it can lead to unauthorized access and potential data breaches. The absence of a proper authentication mechanism or evasion of the existing one can lead to such vulnerabilities.


  • Implement a proper authentication mechanism to ensure that only authorized users can access the OTP validation endpoint.
  • Use a secure communication protocol (e.g., HTTPS) to prevent response tampering during transit.
  • Perform OTP validation on the server-side instead of relying solely on the response from an external service.
  • Validate the response from the OTP validation service to ensure its integrity and authenticity.
  • Consider implementing additional security measures such as rate limiting, request validation, and input sanitization to prevent other types of attacks.

Compliant code

import play.api.mvc._
import play.api.libs.json._
import javax.inject.Inject

class OTPController @Inject()(cc: ControllerComponents, ws: WSClient) extends AbstractController(cc) {

def validateOTP() = Action.async(parse.json) { request =>
val otp = (request.body \\ "otp").as[String]
.withQueryString("otp" -> otp)
.map { response =>
(response.json \\ "success").asOpt[Boolean] match {
case Some(true) => Ok(Json.obj("status" -> "success", "message" -> "OTP validated successfully"))
case _ => BadRequest(Json.obj("status" -> "error", "message" -> "Invalid OTP"))

The updated code includes several changes to address the identified vulnerability:

  1. Secure Communication Protocol: The URL for the OTP validation service now uses HTTPS instead of HTTP. This ensures that the communication between the server and the OTP validation service is encrypted, preventing attackers from tampering with the response during transit.

  2. Server-Side OTP Validation: The OTP validation is now performed asynchronously on the server-side. The server sends a request to the OTP validation service and waits for the response. This prevents attackers from modifying the response of the request to include the success message.

  3. Response Validation: The server now checks the response from the OTP validation service to ensure its integrity and authenticity. If the response includes a success message (i.e., {"success": true}), the server sends a success response to the client. Otherwise, it sends an error response.

  4. Additional Security Measures: Although not shown in the code, it's recommended to implement additional security measures such as rate limiting (to prevent brute-force attacks), request validation (to ensure that the request is well-formed and comes from a legitimate source), and input sanitization (to prevent injection attacks). These measures can further enhance the security of the OTP validation process.