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Firewall Management Essentials: Managing Access Risk

By Mike Rothman

We have discussed two of the three legs of comprehensive firewall management: a change management process and optimizing the rules. Now let’s work through managing risk using the firewall.

Obviously we need to define risk, because depending on your industry and philosophy, risk can mean many different things. For firewall management we are talking about the risk of unauthorized parties accessing sensitive resources. Obviously if a device with critical data is inaccessible to internal and/or external attackers, the risk it presents is lower.

This “access risk management” function involves understanding first and foremost the network’s topology and security controls. The ability to view attack paths provides a visual depiction of how an attacker could gain access to a device. With this information you can see which devices need remediation and/or network workarounds, and prioritize fixes. Another benefit of visualizing attack paths is in understanding when changes on the network or security devices unintentionally expose additional attack surface.

So what does this have to do with your firewall? That’s a logical question, but a key firewall function is access control. You configure the firewall and its rule set to ensure that only authorized ports, protocols, applications, users, etc. have access to critical devices, applications, etc. within your network. A misconfigured firewall can have significant and severe consequences, as discussed in the last post.

For example, years ago when supporting a set of email security devices, we got a call about an avalanche of spam hitting the mailboxes of key employees. The customer was not pleased, but the deployed email security gateway appeared to be working perfectly. Initially perplexed, one of our engineers checked the backup email server, and discovered it was open to Internet traffic due to a faulty firewall rule. So attackers were able to use the back-up server as a mail relay, and blast all the mailboxes in the enterprise. With some knowledge of network topology and the paths between external networks and internal devices, this issue could have been identified and remediated before any employees were troubled.

Key Access Risk Management Features

When examining the network and keeping track of attack paths, look for a few key features:

  1. Topology monitoring: Topology can be determined actively, passively, or both. For active mapping you will want your firewall management tool to pull configurations from firewalls and other access control devices. You also need to account for routing tables, network interfaces, and address translation rules. Interoperating with passive monitoring tools (network behavioral analysis, etc.) can provide more continuous monitoring. You need the ability to determine whether and how any specific device can be accessed, and from where – both internal and external.
  2. Analysis horsepower: Accounting for all the possible paths through a network requires an n_*(_n-1) analysis, and n gets rather large for an enterprise network. The ability to re-analyze millions of paths on every topology change is critical for providing an accurate view.
  3. What if?: You will want to assess each possible change before it is made, to understand its impact on the network and attack surface. This enables the organization to detect additional risks posed by a change before committing it. In the example above, if that customer had a tool to help understand that a firewall rule change would make their backup email server a sitting duck for attackers they would have reconsidered.
  4. Alternative rules: It is not always possible to remediate a specific device due to operational issues. So to control risk you would like a firewall management tool to suggest appropriate rule changes or alternate network routes to isolate the vulnerable device and protect the network.

At this point it should be clear that all these firewall management functions depend on each other. Optimizing rules is part of the change management process, and access risk management comes into play for every change. And vice-versa, so although we discussed these function as distinct requirements of firewall management, in reality you need all of these functions to work together for operational excellence.

In this series’ last post we will focus on getting a quick win with firewall management technology. We will discuss deployment architectures and integration with enterprise systems, and work through a deployment scenario to make many of these concepts a bit more tangible.

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