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Lack of data validation - Type confusion

Need​

Implementation of proper data validation and type checking

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

Description​

Non compliant code​

import play.api.mvc._

object Application extends Controller {
  def process() = Action { request =>
    val data = request.body.asFormUrlEncoded.get("data").head
    val number = Integer.parseInt(data, 16)
    Ok("Processed: " + number)
  }
}

The above Scala code represents a Play Framework application with a single action, process. This action is vulnerable to a type confusion attack due to a lack of proper data validation.

The process method retrieves a form parameter data from the incoming request. It then attempts to parse this parameter as a hexadecimal integer using Integer.parseInt(data, 16).

This is problematic because Integer.parseInt(data, 16) will accept not only regular decimal numbers, but also hexadecimal numbers (e.g., "0xff"). This is a form of type confusion, as the server-side code is interpreting the data in a way that is inconsistent with the expected input type (decimal number).

If the data parameter is expected to only be a decimal number, then accepting hexadecimal numbers can lead to unexpected behavior and potential security vulnerabilities. For example, an attacker could input a large hexadecimal number that causes an integer overflow when parsed.

To fix this vulnerability, the code should validate that the data parameter is a valid decimal number before attempting to parse it.

Steps​

  • Implement proper data validation to ensure that the input is in the expected format.
  • Use regular expressions or specific parsing methods to validate and parse the input.
  • Reject or handle the input appropriately if it does not match the expected format.
  • Avoid directly interpreting or converting the input without proper validation.
  • Consider using a whitelist approach to only allow specific characters or patterns in the input.
  • Sanitize the input by removing any potentially harmful characters or sequences.
  • Implement server-side validation to complement client-side validation.
  • Educate developers about the importance of data validation and secure coding practices.

Compliant code​

import play.api.mvc._
import scala.util.Try

object Application extends Controller {
  def process() = Action { request =>
    val data = request.body.asFormUrlEncoded.get("data").head
    val number = Try(Integer.parseInt(data, 16)).toOption
    number match {
      case Some(num) => Ok("Processed: " + num)
      case None => BadRequest("Invalid data format")
    }
  }
}

The original code was vulnerable due to a lack of data validation. It was directly parsing the input data as a hexadecimal number without checking if the input was in the correct format. This could lead to type confusion if the input was not a valid hexadecimal number.

The fixed code adds data validation using Scala's Try and Option types. The Try block attempts to parse the input data as a hexadecimal number. If the parsing is successful, Try returns a Success containing the parsed number. If the parsing fails (for example, if the input is not a valid hexadecimal number), Try returns a Failure.

The toOption method is then called on the Try result. This converts the Success or Failure to an Option. If the Try was a Success, toOption returns a Some containing the parsed number. If the Try was a Failure, toOption returns None.

The match block then checks the Option. If the Option is Some, the input was a valid hexadecimal number and the number is processed. If the Option is None, the input was not a valid hexadecimal number and a BadRequest response is returned.

This fix ensures that only valid hexadecimal numbers are processed, preventing type confusion. It also provides a clear error response if the input is not in the expected format.

References​

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