Rack is a modular Ruby web server interface. Carefully crafted Range headers can cause a server to respond with an unexpectedly large response. Responding with such large responses could lead to a denial of service issue. Vulnerable applications will use the `Rack::File` middleware or the `Rack::Utils.byte_ranges` methods (this includes Rails applications). The vulnerability is fixed in 3.0.9.1 and 2.2.8.1.