From 17e6f1507b7f2c2a883c180f4f9548445d6dfbda Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Thu, 29 Oct 2015 10:42:44 -0700
Subject: [PATCH] use secure string comparisons for basic auth username /
 password

this will avoid timing attacks against applications that use basic auth.

CVE-2015-7576
---
 .../lib/action_controller/metal/http_authentication.rb     | 7 ++++++-
 activesupport/lib/active_support/security_utils.rb         | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/actionpack/lib/action_controller/metal/http_authentication.rb b/actionpack/lib/action_controller/metal/http_authentication.rb
index 2ac6e37e34..35be6d9300 100644
--- a/actionpack/lib/action_controller/metal/http_authentication.rb
+++ b/actionpack/lib/action_controller/metal/http_authentication.rb
@@ -1,4 +1,5 @@
 require 'base64'
+require 'active_support/security_utils'
 
 module ActionController
   # Makes it dead easy to do HTTP Basic, Digest and Token authentication.
@@ -68,7 +69,11 @@ module ActionController
           def http_basic_authenticate_with(options = {})
             before_action(options.except(:name, :password, :realm)) do
               authenticate_or_request_with_http_basic(options[:realm] || "Application") do |name, password|
-                name == options[:name] && password == options[:password]
+                # This comparison uses & so that it doesn't short circuit and
+                # uses `variable_size_secure_compare` so that length information
+                # isn't leaked.
+                ActiveSupport::SecurityUtils.variable_size_secure_compare(name, options[:name]) &
+                  ActiveSupport::SecurityUtils.variable_size_secure_compare(password, options[:password])
               end
             end
           end
diff --git a/activesupport/lib/active_support/security_utils.rb b/activesupport/lib/active_support/security_utils.rb
index 64c4801179..9be8613ada 100644
--- a/activesupport/lib/active_support/security_utils.rb
+++ b/activesupport/lib/active_support/security_utils.rb
@@ -1,3 +1,5 @@
+require 'digest'
+
 module ActiveSupport
   module SecurityUtils
     # Constant time string comparison.
@@ -16,5 +18,10 @@ module ActiveSupport
       res == 0
     end
     module_function :secure_compare
+
+    def variable_size_secure_compare(a, b) # :nodoc:
+      secure_compare(::Digest::SHA256.hexdigest(a), ::Digest::SHA256.hexdigest(b))
+    end
+    module_function :variable_size_secure_compare
   end
 end