Based on CVE-2018-3760 when the Sprockets server is accidentally being used in production, an attacker can pass in a specifically crafted url that will allow them access to view every file on the system. If the file hit contains a compilable extension such as `.erb` then the code in that file will be executed.

A Rails app will be using the Sprockets file server in production if they have accidentally configured their app to:

```ruby
config.assets.compile = true # Your app is vulnerable
```

It is highly recommended to not use the Sprockets server in production and to instead precompile assets to disk and serve them through a server such as Nginx or via the static file middleware that ships with rails `config.public_file_server.enabled = true`.

This patch mitigates the issue, but explicitly disallowing any requests to any URI resources via the server.