Ruby on Rails XML Processor YAML Deserialization Scanner

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Auxiliary
  include Msf::Exploit::Remote::HttpClient
  include Msf::Auxiliary::Scanner

  def initialize(info={})
    super(update_info(info,
      'Name'        => 'Ruby on Rails XML Processor YAML Deserialization Scanner',
      'Description' => %q{
        This module attempts to identify Ruby on Rails instances vulnerable to
        an arbitrary object instantiation flaw in the XML request processor.
      },
      'Author'      => [
          'hdm', # author
          'jjarmoc' # improvements
          ],
      'License'     => MSF_LICENSE,
      'References'  =>
        [
          ['CVE', '2013-0156'],
          ['URL', 'https://www.rapid7.com/blog/post/2013/01/09/serialization-mischief-in-ruby-land-cve-2013-0156/']
        ]
    ))

    register_options([
      OptString.new('URIPATH', [true, "The URI to test", "/"]),
      OptEnum.new('HTTP_METHOD', [true, 'HTTP Method', 'POST', ['GET', 'POST', 'PUT'] ]),
    ])
  end

  def send_probe(ptype, pdata)
    odata = %Q^<?xml version="1.0" encoding="UTF-8"?>\n<probe type="#{ptype}"><![CDATA[\n#{pdata}\n]]></probe>^
    res = send_request_cgi({
      'uri'    => datastore['URIPATH'] || "/",
      'method' => datastore['HTTP_METHOD'],
      'ctype'  => 'application/xml',
      'data'   => odata
    }, 25)
  end

  def run_host(ip)

    res1 = send_probe("string", "hello")

    unless res1
      vprint_status("#{rhost}:#{rport} No reply to the initial XML request")
      return
    end

    if res1.code.to_s =~ /^[5]/
      vprint_status("#{rhost}:#{rport} The server replied with #{res1.code} for our initial XML request, double check URIPATH")
      return
    end

    res2 = send_probe("yaml", "--- !ruby/object:Time {}\n")

    unless res2
      vprint_status("#{rhost}:#{rport} No reply to the initial YAML probe")
      return
    end

    res3 = send_probe("yaml", "--- !ruby/object:\x00")

    unless res3
      vprint_status("#{rhost}:#{rport} No reply to the second YAML probe")
      return
    end

    vprint_status("Probe response codes: #{res1.code} / #{res2.code} / #{res3.code}")


    if (res2.code == res1.code) and (res3.code != res2.code) and (res3.code != 200)
      print_good("#{rhost}:#{rport} is likely vulnerable due to a #{res3.code} reply for invalid YAML")
      report_vuln({
        :host	=> rhost,
        :port	=> rport,
        :proto  => 'tcp',
        :name	=> self.name,
        :info	=> "Module triggered a #{res3.code} reply",
        :refs   => self.references
      })
    else
      vprint_status("#{rhost}:#{rport} is not likely to be vulnerable or URIPATH & HTTP_METHOD must be set")
    end
  end
end