There’s a URI DoS regression that wasn’t original backported to Ruby 1.9.2. This patch has now been applied and updated on Heroku. Unless you have the patchlevel locked down in your Gemfile, you should get this on your next push. You can read more on the official Ruby news post.
This is the final update to Ruby 1.9.2. Support has officially ended for Ruby 1.9.2 and 1.8.7 on Cedar. We’ll be reaching out to customers still using these Rubies about migrating.