Netdelta – Install and Configure

Netdelta is a tool for monitoring networks and flagging alerts upon changes in advertised services. Now – I like Python and especially Django, and around 2014 or so i was asked to setup a facility for monitoring for changes in that organisation’s perimeter. After some considerable digging, i found nada, as in nothing, apart from a few half-baked student projects. So i went off and coded Netdelta, and the world has never been the same since.

I guess when i started with Netdelta i didn’t see it as a solution that would be widely popular because i was under the impression you could just do some basic shell scripting with nmap, and ndiff is specifically designed for delta flagging. However what became apparent at an early stage was that timeouts are a problem. A delta will be flagged when a host or service times out – and this happens a lot, even on a gigabit LAN, and it happens even more in public clouds. I built some analytics into Netdelta that looks back over the scan history and data and makes a call on the likelihood of a false positive (red, amber green).

Most organisations i worked with would benefit from this. One classic example i can think of – a trading house that had been on an aggressive M&A spree, maybe it was Black Friday or…? Anyway – they fired some network engineers and hired some new and cheaper ones, exacerbating what was already a poorly managed perimeter scenario. CISO wanted to know what was going off with these Internet facing subnets – enter Netdelta. Unauthorised changes are a problem! I am directly aware of no fewer than 6 incidents that occurred as a result of exposed SSH, SMB (Wannacry), and more recently RDP, and indirectly aware of many more.

Anyway without further waffle, here’s how you get Netdelta up and running. Warning – there are a few moving parts, but if someone wants it in Docker, let me know.

I always go with Ubuntu. The differences between Linux distros are like the differences between mueslis. My build was on 18.04 but its highly likely 19 variants will be just fine.

apt-get update
apt-get install curl nmap apache2 python3 python3-pip python3-venv rabbitmq-server mysql-server libapache2-mod-wsgi-py3 git
apt-get -y install software-properties-common
add-apt-repository ppa:certbot/certbot
apt-get install -y python-certbot-apache
Clone the repository from github into your <netdelta root> 
git clone https://github.com/SevenStones/netdelta.git

Filesystem

Create the user that will own <netdelta root>

useradd -s /bin/bash -d /home/<user> -m <user>

Create the directory that will host the Netdelta Django project if necessary

Add the user to a suitable group, and strip world permissions from netdelta directories

 groupadd <group> 
 usermod -G  <group> <user>
 usermod -G  <group> www-data
 chown -R www-data:<group> /var/www
 chown -R <user>:<group> <netdelta root> 

Make the logs dir, e.g. /logs, and you will need to modify /nd/netdelta_logger.py to point to this location. Note the celery monitor logs go to /var/log/celery/celery-monitor.log …which of course you can change.

Strip world permissions from all netdelta and apache root dirs:

chmod -Rv o-rwx <web root>
chmod -Rv o-rwx <netdelta root>

Virtualenv

The required packages are in requirements.txt, in the root of the git repo. Your virtualenv build with Python 3 goes approximately like this …

python3 -m venv /path/to/new/virtual/environment

You activate thusly: source </path/to/new/virtual/environment/>/bin/activate

Then suck in the requirements as root, remembering to fix permissions after you do this.

pip3 install wheel
pip3 install -r <netdelta root>/requirements.txt

You can use whatever supported database you like. MySQL is assumed here.

The Python framework mysqlclient was used with earlier versions of Django and MySQL. but with Python 3 and later Django versions, the word on the street is PyMySQL is the way to go. With this though, it took some trickery to get the Django project up and running; in the form of init.py for the project (<netdelta root>/netdelta/.init.py) and adding a few lines …

import pymysql 
pymysql.install_as_MySQLdb()

While in virtualenv, and under your netdelta root, add a superuser for the DF

Patch libnmap

Two main mods to the libnmap in usage with Netdelta were necessary. First, with later versions of Celery (>3.1), there was a security issue with “deamonic processes are not allowed to have children”, for which an alternative fork of libnmap fixed the problem. Then we needed to return to Netdelta the process id of the running nmap port scanner process.

cd /opt
git clone https://github.com/pyoner/python-libnmap.git
cp ./python-libnmap/libnmap/process.py <virtualenv root>/lib/python3.x/site-packages/libnmap/

then patch libnmap to allow Netdelta to kill scanning processes

<netdelta_root>/scripts/fix-libnmap.bash

Change the environment variables to match your install and use the virtualenv name as a parameter

Database Setup

Create a database called netdetla and use whichever encoding snd collation you like.

CREATE DATABASE netdelta CHARACTER SET utf8 COLLATE utf8_general_ci;

Then from <netdelta root> with virtualenv engaged:

python manage.py makemigrations nd
python manage.py migrate

Web Server

I am assuming all you good security pros don’t want to use the development server? Well as you’re only dealing with port scan data then….your call. I’m assuming Apache as a production web server.

You will need to give Apache a stub web root and enable the wsgi module. For the latter i added this to apache2.conf – this gives you some control over the exact version of Python loaded.

LoadModule wsgi_module "/usr/lib/python3.7/site-packages/mod_wsgi/server/mod_wsgi-py37.cpython-37m-i386-linux-gnu.so"
WSGIPythonHome "/usr"

Under the DocumentRoot line in your apache config file, give the pointers for WSGI.

WSGIDaemonProcess <site> python-home=<virtualenv root> python-path=<netdelta root>  WSGIProcessGroup <site>  WSGIScriptAlias / <netdelta root>/netdelta/wsgi.py  Alias /static/ <netdelta root>/netdelta/

Note also you will need to adjust your wsgi.py under <netdelta root>/netdelta/ –

# Add the site-packages of the chosen virtualenv to work with site.addsitedir('<virtualenv root>/lib/python3.7/site-packages')

Celery

From the current shell
in …<virtualenv> ….under <netdelta root>

celery worker -E -A nd -n default -Q default --loglevel=info -B --logfile=<netdelta root>/logs/celery.log

Under systemd (you will almost certainly want to do this) with the root user. The script pointed to by systemd for

systemctl start celery

can have all the environment checking (this isn’t intended to be a tutorial in BASH scripting), but the core of it…

cd <netdelta root>
nohup $VIRTUALENV_DIR/bin/celery worker -E -A nd -n ${SITE} -Q ${SITE} --loglevel=info -B --logfile=${SITE_LOGS}/celery.log >/dev/null 2>&1 &

And then you can put together your own scripts for status, stop, restart.

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The Art Of The Security Delta: NetDelta

In this article we’ll be answering the following questions:

  • What is NetDelta?
  • Why should i be monitoring for changes in my network(s)?
  • Challenges we faced along the way
  • Other ways of detecting deltas in networks
  • About NetDelta

What Is NetDelta?

NetDelta allows users to configure groups of IP addresses (by department, subnet, etc) and perform one-off or periodic port scans against the configured group, and have NetDelta send alerts when a change is detected.

There’s lot of shiny new stuff out there. APT-buster ™, Silver Bullet ™, etc. Its almost as though someone sits in a room and literally looks for combinations of words that haven’t been used yet and uses this as the driver for a new VC sponsored effort. “Ok ‘threat’ is the most commonly used buzzword currently. Has ‘threat’ been combined with ‘cyber’ and ‘buster’ yet?”, “No”, [hellllooow Benjamin]. The most positive spin we can place on this is that we got so excited about the future while ignoring the present.

These new products are seen as serving the modern day needs of information security, as though the old challenges, going back to day 0 in this sector, or “1998”, have been nailed. Well, how about the old stalwart of Vulnerability Management? The products do not “Manage” anything, they produce lists of vulnerability – this is “assessment”, not “management”. And the lists they produce are riddled with noise (false positives), and what’s worse is there’s a much bigger false negatives problem in that the tools do not cover whole swaths of corporate estates. Doesn’t sound like this is an area that is well served by open source or commercial offerings.

Why Do I Need To Monitor My Networks For Changes?

On the same theme of new products in infosec – how about firewalls (that’s almost as old as it gets)? Well we now have “next-gen” firewalls, but does that mean that old-gen firewalls were phased out, we solved the Network Access Control problem, and then moved on?

How about this: if there is a change in listening services, say in, for example – your perimeter DMZ (!), and you didn’t authorise it, that cannot be a good thing. Its one of either:

  • Hacker/malware activity, e.g. hacker’s connection service (e.g. root shell), or
  • Unauthorised change, e.g. networks ops changed firewall or DMZ host configuration outside of change control
  • You imagined it – perhaps lack of sleep or too much caffeine

Neither of these can be good. They can only be bad. And do we have a way to detect such issues currently?

How does NetDelta help us solve these problems?

Users can configure scans either on a one-off basis, or to be run periodically. So for example, as a user i can tell NetDelta to scan my DMZ perimeter every night at 2 AM and alert me by email if something changed from the previous night’s scan:

  • Previously unseen host comes online in a subnet, either as an unauthorised addition to the group, or unauthorised (rogue) firewall change or new host deployment (maybe an unsanctioned wifi access point or webcam, for example) – these concerns are becoming more valid in the age of Internet of Things (IoT) where devices are shipped with open telnets and so on.
  • Host goes offline – this could be something of interest from a service availability/DoS point of view, as well as the dreaded ‘unauthorised change’.
  • Change in the available services – e.g. hacker’s exploit is successful and manages to locally open a shell on an unfiltered higher port, or new service turned on outside of change control. NetDelta will alert if services are added or removed on a target host.

Host ‘state’ is maintained by NetDelta for as long as the retention period allows, and overall 10 status codes reflect the state of a host over successive periodic scans.

Challenges We Faced With NetDelta

The biggest and only major obstacle is the output of ‘noise’ that results from scan timeouts. With some of the earlier tests scans we noticed that sporadic scan time-outs would occur frequently. This presented a problem (its sort of a false positive) in that a delta is alerted on, but really there hasn’t been a change in listening services or hosts. We increased  the timeout options with nmap but it didn’t help much and only added masses of time on the scans.

The aforementioned issue is one of the issues holding back the nmap ndiff shell script wrapper option, and also ndiff works with XML text files (messy). Shell scripts can work in corporate situations sometimes, but there are problems around the longevity and reliability of the solution. NetDelta is a web-based database (currently MySQL but NoSQL is planned) driven solution with reports and statistics readily available, but the biggest problem with the ndiff option is the scan timeout issues mentioned in the previous paragraph.

NetDelta records host “up” and “down” states and allows the user to configure a number for the number of scans before being considered really down. So if the user chooses 3 as an option, if a target host is down for 3 consecutive scans, it is considered actually down, and a delta is flagged.

Overall the ‘state’ of a host is recorded in the backend database, and the state is a code that reflects a change in the availability or existence of a host. NetDelta has a total of 10 status codes.

Are There Other Ways To Detect NetDeltas?

Remember that we’re covering network services here, i.e. the ‘visibility’ of network services, as they appear to hackers and your customers alike. This is not the same as local host configuration. I can run a netstat command locally to get a list of listening services, but this doesn’t tell me how well my firewall(s) protect me.

  • The ndiff option was covered already
  • Firewall management suites. At least one of these can flag changes in firewall rules, but it still doesn’t give the user the actual “real” view of services. Firewalls can be misconfigured, and they can do unexpected things under certain conditions. The port scanner view of a network is the holy grail effectively – its the absolute/real view that leaves no further room for interpretation and does not require further processing
  • IDS – neither HIDS (host based intrusion detection) nor NIDS (network based intrusion detection) can give a good representation of the view.
  • SIEM – these systems take in logs from other sources so partly by extrapolating from the previous comments, and also with the capability of SIEM itself, it would seem to be a challenge to ask a SIEM to do acrobatics in this area. First of all SIEM is not a cheap solution, but of course this conversation only applies to a case where the organisation already owns a SIEM and can afford the added log storage space, and management overhead, and…of the SIEMs i know, none of them are sufficiently flexible to:
    • take in logs from a port scanning source – theoretically its possible if you could get nmap to speak rsyslogish though, and i’m sure there’s some other acrobatics that are feasible
    • perform delta analysis on those logs and raise an alert

About NetDelta

NetDelta is a Python/Django based project with a MySQL backend (we will migrate to MongoDB – watch this space). Currently at v 1.0, you are most welcome to take part in a trial. We stand on the shoulders of giants:

  • nmap (https://nmap.org/)
  • Python (https://www.python.org/)
  • Django (https://www.djangoproject.com/)
  • Celery (http://www.celeryproject.org/)
  • RabbitMQ (https://www.rabbitmq.com/)
  • libnmap – a Python framework for nmap – (https://github.com/savon-noir/python-libnmap)

Contact us for more info!

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