Need

To prevent unexpected behaviors due to content type misinterpretations

Context

• Usage of Elixir 1.12 for functional programming on the Erlang virtual machine
• Usage of Phoenix Framework 1.6 for web development

Description

Non compliant code

        defmodule PageController do
  use MyApp.Web, :controller

  def index(conn, _params) do
    send_resp(conn, 200, "Hello, world!")
  end
end
        
        

In the insecure code example, the index function responds to a GET request but does not set the Content-Type header. This can lead to misinterpretation of the content type, which can cause unexpected behaviors in clients.

Steps

• Always set the Content-Type header to explicitly define the content types allowed by the application
• Use `put_resp_content_type` function provided by Phoenix framework to set the Content-Type header

Compliant code

        defmodule PageController do
  use MyApp.Web, :controller

  def index(conn, _params) do
    conn
    |> put_resp_content_type("text/plain")
    |> send_resp(200, "Hello, world!")
  end
end
        
        

In the secure code, the index function sets the Content-Type header to text/plain. This informs the client about the type of content in the response, preventing misinterpretations.

References

• 329. Insecure or unset HTTP headers - Content-Type