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Lack of data validation - Header x-amzn-RequestId

Need​

Implementation of robust data validation for the x-amzn-RequestId Header

Context​

  • Usage of Scala for building scalable and functional applications
  • Usage of play.api.mvc for handling HTTP requests and responses in Play Framework

Description​

Non compliant code​

import play.api.mvc._

def processRequest = Action { request =>
  val requestId = request.headers.get("x-amzn-RequestId").getOrElse("")

  // Process the request with the requestId
  // ...
}

In the above Scala code, we are using the Play framework to develop a web application. In the processRequest function, we are trying to get the value of the "x-amzn-RequestId" header from the incoming HTTP request. If the header is not present, we default to an empty string.

The vulnerability here lies in the lack of validation of the "x-amzn-RequestId" header. The code simply accepts whatever value is present in the header without checking if it contains any malicious content. This can lead to a variety of attacks, including but not limited to, SQL Injection, Cross-Site Scripting (XSS), and Command Injection attacks.

For instance, an attacker can send a specially crafted string in the "x-amzn-RequestId" header that can manipulate the SQL query if the requestId is used in a database query. Similarly, if the requestId is reflected back in the response and rendered on the client-side, it can lead to an XSS attack.

Therefore, it's crucial to validate the "x-amzn-RequestId" header before using it in the application.

Steps​

  • Implement server-side validation for the x-amzn-RequestId header
  • Define a whitelist of allowed characters for the requestId
  • Reject or sanitize any requestId that contains potentially dangerous characters
  • Use a regular expression or a validation library to check the requestId against the whitelist
  • Return an appropriate error response if the requestId fails validation

Compliant code​

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

def processRequest = Action { request =>
  val requestId = request.headers.get("x-amzn-RequestId").getOrElse("")
  val requestIdPattern: Regex = "^[a-zA-Z0-9-]*$".r

  requestIdPattern.findFirstIn(requestId) match {
    case Some(_) =>
      // Process the request with the requestId
      // ...
    case None =>
      BadRequest("Invalid x-amzn-RequestId header")
  }
}

The updated code now includes server-side validation for the x-amzn-RequestId header. This is done by defining a whitelist of allowed characters for the requestId using a regular expression. The regular expression ^[a-zA-Z0-9-]*$ only allows alphanumeric characters and hyphens. This is a common pattern for request IDs, but it can be adjusted according to your specific needs.

The findFirstIn method is used to check if the requestId matches the whitelist. If it does, the request is processed as usual. If it doesn't, a BadRequest response is returned with a message indicating that the x-amzn-RequestId header is invalid.

This way, any requestId that contains potentially dangerous characters will be rejected, preventing possible security vulnerabilities.

References​

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