GHSA-m875-3xf6-mf78 unpoly-rails Denial of Service vulnerability

• RubyGems unpoly-rails: < 2.7.2.2 → fixed in 2.7.2.2

There is a possible Denial of Service (DoS) vulnerability in the unpoly-rails gem that implements the Unpoly server protocol for Rails applications. Impact This issues affects Rails applications that operate as an upstream of a load balancer's that uses passive health checks. The unpoly-rails gem echoes the request URL as an `X-Up-Location` response header. By making a request with exceedingly long URLs (paths or query string), an attacker can cause unpoly-rails to write a exceedingly large response header. If the response header is too large to be parsed by a load balancer downstream of the Rails application, it may cause the load balancer to remove the upstream from a load balancing group. This causes that application instance to become unavailable until a configured timeout is reached or until an active healthcheck succeeds. Patches The fixed release 2.7.2.2+ is available via RubyGems and GitHub. Workarounds If you cannot upgrade to a fixed release, several workarounds are available: • Configure your load balancer to use active health checks, e.g. by periodically requesting a route with a known response that indicates healthiness. • Configure your load balancer so the maximum size of response headers is at least twice the maximum size of a URL. • Instead of changing your server configuration you may also configure your Rails application to delete redundant `X-Up-Location` headers set by unpoly-rails: ```ruby class ApplicationController < ActionController::Base after_action :remove_redundant_up_location_header private def remove_redundant_up_location_header if request.original_url == response.headers['X-Up-Location'] response.headers.delete('X-Up-Location') end end end ```