From d61af15199649b110aa66655968295009554db6b Mon Sep 17 00:00:00 2001
From: Joshua Peek <josh@joshpeek.com>
Date: Tue, 28 Oct 2014 12:30:07 -0700
Subject: [PATCH] Check for absolute paths in server URL before passing to find

Various double slashes and URL encodings can bypass current checks.
In the case of the file existing, the server will 500 instead of 403
which leaks the existence but not the contents of the file.

Props to @eadz for finding this.
---
 lib/sprockets/server.rb | 14 +++++++-------
 test/test_server.rb     | 22 ++++++++++++++++++++--
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/lib/sprockets/server.rb b/lib/sprockets/server.rb
index e9c2e5925..e71f41381 100644
--- a/lib/sprockets/server.rb
+++ b/lib/sprockets/server.rb
@@ -33,16 +33,16 @@ def call(env)
       # Extract the path from everything after the leading slash
       path = unescape(env['PATH_INFO'].to_s.sub(/^\//, ''))
 
-      # URLs containing a `".."` are rejected for security reasons.
-      if forbidden_request?(path)
-        return forbidden_response
-      end
-
       # Strip fingerprint
       if fingerprint = path_fingerprint(path)
         path = path.sub("-#{fingerprint}", '')
       end
 
+      # URLs containing a `".."` are rejected for security reasons.
+      if forbidden_request?(path)
+        return forbidden_response
+      end
+
       # Look up the asset.
       asset = find_asset(path, :bundle => !body_only?(env))
 
@@ -90,7 +90,7 @@ def forbidden_request?(path)
         #
         #     http://example.org/assets/../../../etc/passwd
         #
-        path.include?("..")
+        path.include?("..") || Pathname.new(path).absolute?
       end
 
       # Returns a 403 Forbidden response tuple
@@ -222,7 +222,7 @@ def headers(env, asset, length)
       #     # => "0aa2105d29558f3eb790d411d7d8fb66"
       #
       def path_fingerprint(path)
-        path[/-([0-9a-f]{7,40})\.[^.]+$/, 1]
+        path[/-([0-9a-f]{7,40})\.[^.]+\z/, 1]
       end
 
       # URI.unescape is deprecated on 1.9. We need to use URI::Parser
diff --git a/test/test_server.rb b/test/test_server.rb
index 41e263d7c..c5f6a740a 100644
--- a/test/test_server.rb
+++ b/test/test_server.rb
@@ -183,10 +183,28 @@ def app
   end
 
   test "illegal require outside load path" do
-    get "/assets/../config/passwd"
+    get "/assets//etc/passwd"
     assert_equal 403, last_response.status
 
-    get "/assets/%2e%2e/config/passwd"
+    get "/assets/%2fetc/passwd"
+    assert_equal 403, last_response.status
+
+    get "/assets//%2fetc/passwd"
+    assert_equal 403, last_response.status
+
+    get "/assets/%2f/etc/passwd"
+    assert_equal 403, last_response.status
+
+    get "/assets/../etc/passwd"
+    assert_equal 403, last_response.status
+
+    get "/assets/%2e%2e/etc/passwd"
+    assert_equal 403, last_response.status
+
+    get "/assets/.-0000000./etc/passwd"
+    assert_equal 403, last_response.status
+
+    get "/assets/.-0000000./etc/passwd"
     assert_equal 403, last_response.status
   end