Ask The Experts: Why Do Security Testing of Internal Computer Networks?

Monday, November 03, 2014

Brent Huston

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Most organizations have realized the need to have vulnerability assessments of their internet-facing (external) computer networks performed periodically. Maybe they are alarmed by all the data compromises they hear about on the news or perhaps they are subject to regulatory guidance and are required to have vulnerability assessments done. But many organizations draw the line there and never have the security of their internal networks tested. This is a mistake! At least it’s a mistake if your goal is actually to protect your computer systems and the private information they store and process.

It is true that the most attacks against information systems come from external attackers, but that does not mean the internal threat is negligible. About one sixth of data compromises are due to employees and privileged insiders such as service providers and contractors. But there are many other reasons for testing the security of your internal networks besides the internal threat. For one thing, once cyber-criminals find a hole in your external defenses they are suddenly “insiders” too. And if your internal systems are not configured correctly, hardened and monitored, it becomes trivial for these attackers to own your systems and compromise all the private information you have.

The type of testing that gives you the most bang for the buck is internal vulnerability assessment. Doing this type of testing regularly has many benefits. One benefit that people usually don’t associate with internal vulnerability assessment is that it can be used to make maps and inventories of the network. These are essentials of information security. After all, if you don’t know what you have on your network and where it is, how can you protect it? Another benefit is that it allows you to view your internal network with perspective. In other words, it lets you see it the way an attacker would. It will reveal:

  • Access control issues such as default and blank passwords mistakenly left on the network during administration, open files shares or anonymous FTP sites that may contain private data or user accounts that are suspicious or inappropriate.
  • Systems that are missing security patches or that are running out of date software or operating systems that are no longer supported by the vendors.
  • Systems that have been misconfigured or that reveal too much information to unauthorized users.
  • Ports that are inappropriately left open or dangerous services such as Telnet or Terminal Services present on the network.
  • Poor network architecture that fails to properly segment and enclave information assets so that only those with a business need can access them.
  • How well third party systems present on your network are patched, updated and secured.

Also, from a business perspective, performing regular internal vulnerability assessments shows your customers that you are serious about information security; a factor that could influence them to choose your organization over others.

In addition to vulnerability testing, it is also more than just desirable to have penetration testing of the internal network performed occasionally. While vulnerability assessment shows you what flaws are available for attackers to exploit (the width of your security exposure), penetration testing shows you what attackers can actually do with those flaws to compromise your systems and data (the depth of your security exposure). Internal penetration testing can:

  • Reveal how attackers can exploit combinations of seemingly low risk vulnerabilities to compromise whole systems or networks (cascading failures).
  • Show you if the custom software applications you are using are safe from compromise.
  • Show you not only what is bad about your network security measures, but what is working well (this can really save you money and effort by helping you chose only the most effective security controls).

One other type of penetration testing that is well worth the time and expense is social engineering testing. As network perimeters become increasingly secure, social engineering techniques such as Phishing emails or bogus phone calls are being used more and more by attackers to gain a foothold on the internal network. We at MSI are very aware of just how often these techniques work. How well do you think your employees would resist such attacks?

Thanks to John Davis for this post.

This was cross-posted from the MSI State of Security blog.

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Ian Tibble Yes, its always been important, i just wouldn't really bother with unauthenticated internal vulnerability testing...too many false -ves. A Vulnerability Management program utilising credentialed scans - this is getting closer.
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