Foreman » Smart Proxy

WEBrick by default is configured with a verbose HTTP server header that includes key information about the server. While this isn't the most significant information disclosure vulnerability in isolation, the relative obscurity of WEBrick in production environments and the use of non-standard HTTP ports make identifying publicly facing Smart Proxy servers trivial. I was able to find ~400 publicly facing servers in a few minutes using Shodan.

Example header: "WEBrick/1.3.1 (Ruby/2.0.0/2014-11-13) OpenSSL/1.0.1e"
Shodan search: https://www.shodan.io/search?query=WEBrick+X-Cascade%3A+pass+port%3A"8443"