1 files changed, 1 insertions, 1 deletions

diff --git a/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb b/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
index 3e5d23b5c1..09dd08898c 100644
--- a/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
+++ b/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
@@ -170,7 +170,7 @@ module HTML
 
     def contains_bad_protocols?(attr_name, value)
       uri_attributes.include?(attr_name) &&
-      (value =~ /(^[^\/:]*):|(&#0*58)|(&#x70)|(%|%)3A/ && !allowed_protocols.include?(value.split(protocol_separator).first))
+      (value =~ /(^[^\/:]*):|(&#0*58)|(&#x70)|(%|%)3A/ && !allowed_protocols.include?(value.split(protocol_separator).first.downcase))
     end
   end
 end