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List:       oss-security
Subject:    [oss-security] Arbitrary file existence disclosure in Sprockets (CVE-2014-7819)
From:       Aaron Patterson <tenderlove () ruby-lang ! org>
Date:       2014-10-30 18:52:56
Message-ID: 20141030185256.GC71386 () TC ! local
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Arbitrary file existence disclosure in Sprockets

There is an information leak vulnerability in Sprockets. This vulnerability
has been assigned the CVE identifier CVE-2014-7819.

Versions Affected:  ALL
Not affected:       NONE
Fixed Versions:     2.12.X

Impact
------
Specially crafted requests can be used to determine whether a file exists on
the filesystem that is outside an application's root directory.  The files will not be served, \
but attackers can determine whether or not the file exists.

All users running an affected release should either upgrade or use one of the work arounds \
immediately.

Releases 
-------- 
The 2.12.X releases are available at the normal locations. 

Workarounds 
----------- 
In Rails applications, work around this issue, set config.serve_static_assets = false in an \
initializer.  This work around will not be possible in all hosting environments and upgrading \
is advised.

Patches 
------- 
To aid users who aren't able to upgrade immediately we have provided patches for the two \
supported release series.  They are in git-am format and consist of a single changeset. 

* 2-12-sec-static-files.patch - Patch for the 2.12.x release series

Credits 
------- 

This vulnerability was reported by multiple researchers working independently.  Thanks to each \
of them for reporting the issue to us and verifying the fixes.

* Eaden McKee
* Dennis Hackethal & Christian Hansen of Crowdcurity
* Juan C. Müller & Mike McClurg of Greenhouse.io 
* Alex Ianus of Coinbase

-- 
Aaron Patterson
http://tenderlovemaking.com/


["2-12-sec-static-files.patch" (text/plain)]

From 9c9da3b8a25174721a04e988f904b7dc3d7343d1 Mon Sep 17 00:00:00 2001
From: Joshua Peek <josh@joshpeek.com>
Date: Wed, 15 Oct 2014 11:59:48 -0700
Subject: [PATCH 1/3] 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 e9c2e59..e71f413 100644
--- a/lib/sprockets/server.rb
+++ b/lib/sprockets/server.rb
@@ -33,16 +33,16 @@ module Sprockets
       # 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 @@ module Sprockets
         #
         #     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 @@ module Sprockets
       #     # => "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 41e263d..c5f6a74 100644
--- a/test/test_server.rb
+++ b/test/test_server.rb
@@ -183,10 +183,28 @@ class TestServer < Sprockets::TestCase
   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

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