Add hardened headers to user-uploaded files

config/application.rb

@@ -161,6 +161,10 @@ module Mastodon
 
     config.active_record.yaml_column_permitted_classes = [Symbol, Date, Time, ActiveSupport::HashWithIndifferentAccess, ActiveSupport::TimeWithZone, ActiveSupport::TimeZone]
 
+    config.public_file_server.headers = {
+      'X-Content-Type-Options' => 'nosniff',
+    }
+
     # config.paths.add File.join('app', 'api'), glob: File.join('**', '*.rb')
     # config.autoload_paths += Dir[Rails.root.join('app', 'api', '*')]
 

dist/nginx.conf

@@ -61,12 +61,15 @@ server {
   location ~ ^/(emoji|packs|system/accounts/avatars|system/media_attachments/files) {
     add_header Cache-Control "public, max-age=31536000, immutable";
     add_header Strict-Transport-Security "max-age=31536000" always;
+    add_header X-Content-Type-Options nosniff;
+    add_header Content-Security-Policy "default-src 'none'; form-action 'none'";
     try_files $uri @proxy;
   }
 
   location /sw.js {
     add_header Cache-Control "public, max-age=0";
     add_header Strict-Transport-Security "max-age=31536000" always;
+    add_header X-Content-Type-Options nosniff;
     try_files $uri @proxy;
   }