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Lack of data validation - Headers

Need​

Implementation of robust data validation for HTTP headers

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 index = Action { request =>
  val username = request.headers.get("username").getOrElse("Guest")
  Ok("Hello " + username)
}

The above code snippet represents a controller action in a Scala application using the Play Framework. The index function is an HTTP endpoint that fetches the "username" from the request headers and directly uses it to construct an HTTP response.

The vulnerability here lies in the lack of validation for the "username" header. The code simply fetches the value of the "username" header and uses it without any data sanitization or validation. This means that an attacker could potentially inject malicious values into the "username" header to perform Cross-Site Scripting (XSS) attacks or compromise the integrity of the stored information.

For example, if an attacker sends a request with the "username" header set to <script>alert('XSS')</script>, the server would respond with Hello <script>alert('XSS')</script>. If this response is then rendered in a web page without proper output encoding, the script would execute, leading to an XSS attack.

Therefore, it is crucial to validate and sanitize all user input, including HTTP headers, to prevent such vulnerabilities.

Steps​

  • Implement data validation for the 'username' header
  • Use a whitelist approach to validate the allowed values for the 'username' header
  • Sanitize the input to prevent any potential XSS attacks
  • Consider using a library or framework-provided functionality for data validation and sanitization

Compliant code​

import play.api.mvc._
import org.apache.commons.lang3.StringEscapeUtils

def index = Action { request =>
  val username = request.headers.get("username").getOrElse("Guest")
  val sanitizedUsername = StringEscapeUtils.escapeHtml4(username)
  if (isValidUsername(sanitizedUsername)) {
    Ok("Hello " + sanitizedUsername)
  } else {
    BadRequest("Invalid username")
  }
}

def isValidUsername(username: String): Boolean = {
  val allowedUsernames = List("Guest", "Admin", "User") // Add more allowed usernames here
  allowedUsernames.contains(username)
}

The updated code includes a function isValidUsername that checks if the provided username is in the list of allowed usernames. This is a whitelist approach to data validation, which is generally more secure than a blacklist approach because it explicitly defines what is allowed.

The username is also sanitized using the StringEscapeUtils.escapeHtml4 method from the Apache Commons Lang library. This method escapes any special characters that could be used to perform an XSS attack, such as &lt;, >, &, ', and ". This way, even if an attacker tries to inject malicious code into the 'username' header, the code will be escaped and rendered harmless.

If the username is not valid, the server responds with a 400 Bad Request status code. This gives the client clear feedback that the request was not processed due to invalid input.

Please note that the list of allowed usernames is just an example. In a real application, you would probably want to check the username against a database of registered users. Also, the Apache Commons Lang library is used here for simplicity, but the Play framework may provide its own utilities for escaping HTML that you could use instead.

References​

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