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Lack of data validation - Input Length

Need​

Enforce input length validation to prevent excessive data submission

Context​

  • Usage of Scala for functional and object-oriented programming in the JVM
  • 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 index = Action(parse.text) { request =>
    Ok("Got: " + request.body)
  }
}

In the above Scala code snippet, which uses the Play Framework, we have an endpoint that is vulnerable to attacks due to the lack of input length validation. The index endpoint accepts any text as input and directly uses it in the response.

The Action(parse.text) part of the code is where the vulnerability lies. It parses the request body as text without any restriction on the length of the input.

This means that an attacker could potentially send a massive amount of characters in the body of the request, which could lead to various issues such as:

  • Buffer overflow: If the application tries to store the input in a buffer that isn't large enough, it could overflow and overwrite adjacent memory, potentially leading to erratic program behavior or even code execution.
  • Denial of Service (DoS): If the application tries to process a very large input, it could consume a lot of resources (CPU, memory), slowing down the system or even crashing it, thus denying service to legitimate users.
  • Injection attacks: If the input is used in a context where it is interpreted as code (e.g., SQL, OS command), an attacker could inject malicious code.

Therefore, it's crucial to validate the length of the input and reject any input that is suspiciously large.

Steps​

  • Implement input length validation on the endpoint
  • Define a maximum allowed length for the input
  • Check the length of the request body and reject requests that exceed the maximum length
  • Return an appropriate error response when the input length exceeds the limit

Compliant code​

import play.api.mvc._

object Application extends Controller {
  val MaxLength = 1000 // Define your maximum length here

  def index = Action(parse.text(MaxLength)) { request =>
    request.body.length match {
      case length if length > MaxLength =>
        BadRequest("Request body exceeds maximum allowed length")
      case _ =>
        Ok("Got: " + request.body)
    }
  }
}

The updated code introduces a maximum length limit for the request body. This is done by defining a constant MaxLength and using it as a parameter to the parse.text method. This ensures that the request body will not exceed the specified length.

In the action block, we check the length of the request body. If it exceeds MaxLength, we return a BadRequest response with an appropriate error message. This effectively rejects any requests that try to send more data than is allowed.

If the length of the request body is within the limit, we proceed as before, returning an Ok response with the request body.

This change addresses the vulnerability by enforcing a strict limit on the size of the request body, thus preventing potential attackers from sending massive amounts of characters and expanding attack vectors.

References​

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