From 9c34fa05900b968d74f08ccf40917848a7be9441 Mon Sep 17 00:00:00 2001
From: schneems <richard.schneeman+foo@gmail.com>
Date: Tue, 24 Apr 2018 16:32:22 -0500
Subject: [PATCH] Do not respond to http requests asking for a `file://`

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.
---
 test/test_server.rb     | 7 +++++++
 1 file changed, 7 insertions(+), 0 deletion(-)

diff --git a/test/test_server.rb b/test/test_server.rb
index 66429533..19921e19 100644
--- a/test/test_server.rb
+++ b/test/test_server.rb
@@ -320,6 +320,13 @@ def app
     assert_equal 403, last_response.status
   end
 
+  test "illegal access of a file asset" do
+    absolute_path = fixture_path("server/app/javascripts")
+
+    get "assets/file:%2f%2f//#{absolute_path}/foo.js"
+    assert_equal 403, last_response.status
+  end
+
   test "add new source to tree" do
     filename = fixture_path("server/app/javascripts/baz.js")