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Insecurely generated token - Validation

Need​

Secure token generation and validation

Context​

  • Usage of Scala for building scalable and functional applications
  • Usage of play.api.mvc for handling HTTP requests in Play Framework
  • Usage of play.api.libs.json for JSON parsing and manipulation in Play Framework
  • Usage of scala.concurrent.ExecutionContext for managing concurrent execution in Scala applications
  • Usage of javax.inject.Inject for dependency injection in Java applications

Description​

Non compliant code​

import play.api.mvc._
import play.api.libs.json._
import scala.concurrent.ExecutionContext
import javax.inject.Inject

class UserController @Inject()(cc: ControllerComponents)(implicit ec: ExecutionContext) extends AbstractController(cc) {
  
  def createUser = Action(parse.json) { request =>
    val token = (request.headers.get("token")).getOrElse("")
    val algorithm = (request.headers.get("algorithm")).getOrElse("HS256")
    
    val header = Json.obj(
      "alg" -> algorithm,
      "typ" -> "JWT"
    )

    val payload = request.body
    val signature = java.util.Base64.getEncoder.encodeToString((header.toString() + payload.toString()).getBytes())

    if (token == signature) {
      Ok("User created successfully")
    } else {
      BadRequest("Invalid token")
    }
  }
}

In the above code, we have a createUser method in UserController which is vulnerable to insecure token validation. The createUser method accepts a JSON request and retrieves the token and algorithm from the request headers.

The vulnerability lies in the fact that the algorithm used for token validation is taken directly from the request headers without any checks. This means an attacker can modify the 'algorithm' header to bypass the token signature validation.

The createUser method then creates a header JSON object with the algorithm and token type, and a payload from the request body. It then creates a signature by encoding the string representation of the header and payload using Base64.

The method then compares the token from the request headers with the generated signature. If they match, it sends a response indicating successful user creation; otherwise, it sends a 'Invalid token' response.

This is insecure as an attacker can manipulate the 'algorithm' header to an invalid or non-existent algorithm, which would bypass the signature validation. This could allow the attacker to create users without a valid token.

Steps​

  • Use a secure and reliable token generation library or framework that handles token validation.
  • Avoid manually generating the token signature by concatenating the header and payload. Instead, use the token generation library or framework to generate the signature.
  • Ensure that the token algorithm is securely configured and cannot be modified by the user. Use a predefined and secure algorithm for token encryption.
  • Implement proper token validation logic to verify the integrity and authenticity of the token. This may involve verifying the signature, checking the token expiration, and validating any additional claims or attributes.
  • Consider using a secure token storage mechanism to prevent token tampering or unauthorized access.

Compliant code​

import play.api.mvc._
import play.api.libs.json._
import scala.concurrent.ExecutionContext
import javax.inject.Inject
import pdi.jwt.{JwtAlgorithm, JwtJson}
import play.api.Configuration

class UserController @Inject()(cc: ControllerComponents, config: Configuration)(implicit ec: ExecutionContext) extends AbstractController(cc) {
  
  private val secretKey = config.get[String]("jwt.secret")
  private val algorithm = JwtAlgorithm.HS256

  def createUser = Action(parse.json) { request =>
    val token = (request.headers.get("token")).getOrElse("")
    
    val isValidToken = JwtJson.isValid(token, secretKey, Seq(algorithm))

    if (isValidToken) {
      Ok("User created successfully")
    } else {
      BadRequest("Invalid token")
    }
  }
}

The updated code uses the pdi.jwt library, a secure and reliable library for handling JSON Web Tokens (JWT) in Scala. This library provides methods for generating and validating JWTs, which helps to prevent insecure token generation and validation.

The secretKey and algorithm are now securely configured and cannot be modified by the user. The secretKey is retrieved from the application's configuration, and the algorithm is set to HS256, a secure algorithm for JWT encryption.

The createUser method now uses the JwtJson.isValid method from the pdi.jwt library to validate the token. This method verifies the token's signature, checks the token's expiration (if any), and validates the token's claims. If the token is valid, the method returns Ok("User created successfully"). If the token is not valid, the method returns BadRequest("Invalid token").

This updated code helps to prevent the insecure token generation and validation vulnerability by using a secure token generation and validation library, securely configuring the token algorithm, and implementing proper token validation logic.

References​

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