Strip [nil] from parameters hash.

Thanks to Ben Murphy for reporting this!

CVE-2012-2660

actionpack/lib/action_dispatch/http/request.rb

@@ -247,6 +247,28 @@ module ActionDispatch
       LOCALHOST.any? { |local_ip| local_ip === remote_addr && local_ip === remote_ip }
     end
 
+    protected
+
+    # Remove nils from the params hash
+    def deep_munge(hash)
+      hash.each_value do |v|
+        case v
+        when Array
+          v.grep(Hash) { |x| deep_munge(x) }
+        when Hash
+          deep_munge(v)
+        end
+      end
+
+      keys = hash.keys.find_all { |k| hash[k] == [nil] }
+      keys.each { |k| hash[k] = nil }
+      hash
+    end
+
+    def parse_query(qs)
+      deep_munge(super)
+    end
+
     private
 
     def check_method(name)

actionpack/test/dispatch/request/query_string_parsing_test.rb

@@ -81,7 +81,12 @@ class QueryStringParsingTest < ActionDispatch::IntegrationTest
   end
 
   test "query string without equal" do
-    assert_parses({ "action" => nil }, "action")
+    assert_parses({"action" => nil}, "action")
+    assert_parses({"action" => {"foo" => nil}}, "action[foo]")
+    assert_parses({"action" => {"foo" => { "bar" => nil }}}, "action[foo][bar]")
+    assert_parses({"action" => {"foo" => { "bar" => nil }}}, "action[foo][bar][]")
+    assert_parses({"action" => {"foo" => nil}}, "action[foo][]")
+    assert_parses({"action"=>{"foo"=>[{"bar"=>nil}]}}, "action[foo][][bar]")
   end
 
   test "query string with empty key" do