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Network Security in the Age of *Any* Computing: Containing Access

By Mike Rothman

In the first post of this series, we talked about the risks inherent to this concept of any computing, where those crazy users want to get at critical data at any time, from anywhere, on any device. And we all know it’s not pretty. Sure, there are things we can do at the device layer to protect the and ensure a proper configurations. But in this series we will focus on how to architect and secure the network to protect critical data. The first aspect of that is restricting access to key portions of your network to only those folks that need it.

Segmentation is your friend

There is an old saying, “out of sight, out of mind,” which could be rephrased for information security as, “out of reach, out of BitTorrent.” By using a smart network segmentation strategy, you can keep the critical data out of the clutches of attackers. OK, that’s an overstatement, but segmentation is the first step to protecting key data.

We want to make it as hard as possible for the data to be compromised, and that’s why we put up as many obstacles as possible for attackers. Unless you are being specifically targeted, simply not being the path of least resistance is a decent strategy. The fewer folks who have access to something, the less likely that access will be abused, and the more quickly and effectively we can figure out who is the bad actor in case of malfeasance. Not that we believe the PCI-DSS v2.0 standards represent even a low bar for security controls, but they do advocate and require segmentation of cardholder data. Here is the specific language:

All systems must be protected from unauthorized access from untrusted networks, whether entering the system via the Internet as e-commerce, employee Internet access through desktop browsers, employee e-mail access, dedicated connections such as business-to-business connections, via wireless networks, or via other sources. Often, seemingly insignificant paths to and from untrusted networks can provide unprotected pathways into key systems. Firewalls are a key protection mechanism for any computer network.

One architectural construct to think about segmentation is the idea of vaults, which really are just a different way of thinking about segmentation of all data – not just cardholder data. This entails classifying data sources into a few tiers of sensitivity and then designing a control set to ensure access to only those authorized.

The goal behind classifying critical data sources is to ensure access is only provided to the right person, on the right device, from the right place, at the right time. Of course, that first involves defining rules for who can come in, from where, when, and on what device. And we cannot trivialize that effort, because it’s time consuming and difficult. But it needs to be done.

Once the data is classified and the network is segmented – which will discuss in more depth as we progress through this series – we need to authenticate the user. An emerging means of enforcing access to only those authorized devices is to look at something like risk-based or adaptive authentication, where the authentication isn’t just about two or more factors, but instead dynamically evaluated based on any number of data points: including who you are, what you are doing, where you are connecting from, and when you are trying to gain access.

This certainly works well for ensuring only the right folks get in, but what happens once they are in? The obvious weakness of a control structure focused purely on initial authentication is that a device could be compromised after entry – and then all the network controls are irrelevant because the device already has unfettered access. A deeper look at risk-based authentication is beyond our scope for this research project, but warrants investigation as you design control structures.

We also need to ensure we are very critically looking at how the network controls can be bypassed. If a machine is compromised after getting access, that is a problem unless you are constantly scrutinizing who has access on a continuous basis. And yes, we’ll discuss that in the next post. You also need to worry about unauthorized physical access to your network. That could be a hijacked physical port or a rogue wireless access point. Either way, someone then gets physical access to your network and bypasses the perimeter controls.

Architectural straw man

3 use models for network accessNow let’s talk about one architectural construct in terms of three different use models for your network, and how to architect a network in three segments, depending on the use case for access.

  1. Corporate network: This involves someone who has physical access to your corporate network. Either via a wired connection or a wireless access point.
  2. External mobile devices: These devices access corporate resources via an uncontrolled network. That includes home networks, public wireless networks, cellular (3G) networks, and even partner networks. If your network security team can’t see the entirety of the ingress path, then you need to consider it an external connection and device.
  3. Internal guest access: These are devices that just need to access the Internet from inside one of your facilities. Typically these are smartphones used by employees, but we must also factor in a use case for businesses (retail/restaurants, healthcare facilities, etc.) to provide access as a service.

We want to provide different (and increasing) numbers of hoops for users to jump through to get access to important data. The easiest to discuss is the third case (internal guest access), because you only need to provide an egress pipe for those folks. We recommend total physical isolation for these devices. That means a totally separate (overlay) wireless network, which uses a different pipe to the Internet. Yes, that’s more expensive. But you don’t want a savvy attacker figuring out a way to jump from the egress network to the internal network. If the networks are totally separate, you eliminate that risk.

The techniques to support your corporate network and external mobile devices are largely the same under the philosophy of “trust, but verify.” So we need to design the control sets to scrutinize users. The real question is how many more hoops to you put in place for an external device versus one with physical access. And how to classify the data to establish tiers of sensitivity. As we continue through this series, we will evaluate what these controls can and should be, and consider technologies to implement these control structures.

The next post will zero in on enforcing segmentation with specific technologies, weighing pros and cons of different options. As always, we look forward to your comments on what we are missing, and where our models fall short.

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