I don’t typically blog about network engineering here. However, in the last few weeks I’ve seen several major companies get hit with ransomware attacks. While this isn’t an uncommon thing in 2019, it is uncommon that their entire environments were taken offline because of it. So with that, let’s talk about how these attacks can do this. Since the best way to deal with any sort of an attack is to deal with an “Assume breach” model, let’s talk about the best way to defend against attacks: physical network security.
The Attack Vector: Dumb Humans
The easiest way to attack any company is via human targets. Whether it’s bribing a sysadmin to get credentials, or a standard phishing attack, or any sort of other malware, the best way to pwn a company is by getting an unknowing (or knowing) human to most of the work for you. There are ways to stop these sorts of things from getting in the front door–the first would be to use an email service like Office 365 or GMail, that have built-in phishing protections, and use machine learning based on their mass volume of exposure to attacks, that protect you. You should also educate your users to avoid these scams–there is good training that I’ve taken for a few clients that do this.
But the real assumption is to take an assume breach methodology. I’m currently working on a financial system for a Fortune 100 company. In order to reach the servers, I have to use a special locked down laptop, have two key cards, and go through two jump hosts to get there. Even if that laptop were to get hacked (and it wouldn’t because you can’t install software on it) you couldn’t do anything without my key cards and PINs.
Physical and Virtual Network Security
Can you connect to your production database servers over any port from your desktop? Or to your domain controllers? If you can do that you have a problem. Because once someone’s desktop gets pwned, then the malicious software that gets installed when the CEO tries to open a PDF with the new Taylor Swift album on it, can then run anywhere on your network. This is bad.
The IBM white paper linked above is the gold standard of how to build and segment your network. In a common example there a few zones:
Black Zone: No outbound external traffic, inbound restricted to whitelisted IPs and ports from with in black and green zones. This is where your domain controllers and database servers with any sort of sensitive data should live.
Green Zone: Limited external traffic (think Windows Update, Power BI gateway, Linux package repos), can communicate to end use networks over controlled ports. This is where most of your application servers and some management services should live.
Blue Zone: Management zone–this is where you should have your jump boxes so that you don’t have to log directly onto production boxes. This can have limited external traffic, and should be able to talk to the servers in the black zones, but only over ports that you have specified.
Yellow Zone: This is typically where your DMZ will exist. That means you are allowing inbound traffic from the internet. This is obviously a big attack vector, which means it should live on an isolated sector of your network, and the traffic to and from this zone should be locked down to specific IPs and ports that need connectivity.
Red Zone: This is where the users live. There’s internet access, but communications from this network should nearly always stay within this network. You will have teams that want to deploy production workloads in this network. Don’t let them.
But That Sounds Hard
Good security is always hard. See my above server management issues. In my scenario, when the CEO got pwned you might have to deal with a bunch of ransomware laptops, but since your servers and domain controllers weren’t easily reachable from the desktop network, your company would keep moving, and you could simply re-image the pwned machines.
This is Trivial to Implement with Cloud Networks
In order to do this on-premises, you may have to buy a lot more networking gear than you already have, or at least restructure a whole lot of virtual lans (vLANs). However, in a cloud scenario, or even in some virtual infrastructures this kind of model is trivial to implement. Just look up network security zones in Azure (and you never have to run any cable in the cloud).
Technology, and especially enterprise technology isn’t easy, but it’s more important than ever to use good security methods across your environment.
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