3 files changed, 7 insertions, 4 deletions
diff --git a/actionpack/lib/action_dispatch/middleware/debug_exceptions.rb b/actionpack/lib/action_dispatch/middleware/debug_exceptions.rb
index d42b35a4cf..18852b0a57 100644
--- a/actionpack/lib/action_dispatch/middleware/debug_exceptions.rb
+++ b/actionpack/lib/action_dispatch/middleware/debug_exceptions.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative "../http/request"
 require_relative "exception_wrapper"
 require_relative "../routing/inspector"
@@ -21,7 +22,7 @@ module ActionDispatch
         if clean_params.empty?
           "None"
         else
-          PP.pp(clean_params, "", 200)
+          PP.pp(clean_params, "".dup, 200)
         end
       end
 
diff --git a/actionpack/lib/action_dispatch/middleware/ssl.rb b/actionpack/lib/action_dispatch/middleware/ssl.rb
index 557721c301..e79404c993 100644
--- a/actionpack/lib/action_dispatch/middleware/ssl.rb
+++ b/actionpack/lib/action_dispatch/middleware/ssl.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module ActionDispatch
   # This middleware is added to the stack when `config.force_ssl = true`, and is passed
   # the options set in `config.ssl_options`. It does three jobs to enforce secure HTTP
@@ -94,7 +95,7 @@ module ActionDispatch
 
       # http://tools.ietf.org/html/rfc6797#section-6.1
       def build_hsts_header(hsts)
-        value = "max-age=#{hsts[:expires].to_i}"
+        value = "max-age=#{hsts[:expires].to_i}".dup
         value << "; includeSubDomains" if hsts[:subdomains]
         value << "; preload" if hsts[:preload]
         value
@@ -133,7 +134,7 @@ module ActionDispatch
         host = @redirect[:host] || request.host
         port = @redirect[:port] || request.port
 
-        location = "https://#{host}"
+        location = "https://#{host}".dup
         location << ":#{port}" if port != 80 && port != 443
         location << request.fullpath
         location
diff --git a/actionpack/lib/action_dispatch/middleware/static.rb b/actionpack/lib/action_dispatch/middleware/static.rb
index fb99f13a1c..6f4a97da3e 100644
--- a/actionpack/lib/action_dispatch/middleware/static.rb
+++ b/actionpack/lib/action_dispatch/middleware/static.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rack/utils"
 require "active_support/core_ext/uri"
 
@@ -33,7 +34,7 @@ module ActionDispatch
       paths = [path, "#{path}#{ext}", "#{path}/#{@index}#{ext}"]
 
       if match = paths.detect { |p|
-        path = File.join(@root, p.force_encoding(Encoding::UTF_8))
+        path = File.join(@root, p.dup.force_encoding(Encoding::UTF_8))
         begin
           File.file?(path) && File.readable?(path)
         rescue SystemCallError