Is Penetration Testing Worth it?

By Bruce Schneier
Information Security
March 2007

This essay appeared as the first half of a point-counterpoint with Marcus Ranum. Marcus's side can be found on his website.

There are security experts who insist penetration testing is essential for network security, and you have no hope of being secure unless you do it regularly. And there are contrarian security experts who tell you penetration testing is a waste of time; you might as well throw your money away. Both of these views are wrong. The reality of penetration testing is more complicated and nuanced.

Penetration testing is a broad term. It might mean breaking into a network to demonstrate you can. It might mean trying to break into a network to document vulnerabilities. It might involve a remote attack, physical penetration of a data center or social engineering attacks. It might use commercial or proprietary vulnerability scanning tools, or rely on skilled white-hat hackers. It might just evaluate software version numbers and patch levels, and make inferences about vulnerabilities.

It's going to be expensive, and you'll get a thick report when the testing is done.

And that's the real problem. You really don't want a thick report documenting all the ways your network is insecure. You don't have the budget to fix them all, so the document will sit around waiting to make someone look bad. Or, even worse, it'll be discovered in a breach lawsuit. Do you really want an opposing attorney to ask you to explain why you paid to document the security holes in your network, and then didn't fix them? Probably the safest thing you can do with the report, after you read it, is shred it.

Given enough time and money, a pen test will find vulnerabilities; there's no point in proving it. And if you're not going to fix all the uncovered vulnerabilities, there's no point uncovering them. But there is a way to do penetration testing usefully. For years I've been saying security consists of protection, detection and response--and you need all three to have good security. Before you can do a good job with any of these, you have to assess your security. And done right, penetration testing is a key component of a security assessment.

I like to restrict penetration testing to the most commonly exploited critical vulnerabilities, like those found on the SANS Top 20 list. If you have any of those vulnerabilities, you really need to fix them.

If you think about it, penetration testing is an odd business. Is there an analogue to it anywhere else in security? Sure, militaries run these exercises all the time, but how about in business? Do we hire burglars to try to break into our warehouses? Do we attempt to commit fraud against ourselves? No, we don't.

Penetration testing has become big business because systems are so complicated and poorly understood. We know about burglars and kidnapping and fraud, but we don't know about computer criminals. We don't know what's dangerous today, and what will be dangerous tomorrow. So we hire penetration testers in the belief they can explain it.

There are two reasons why you might want to conduct a penetration test. One, you want to know whether a certain vulnerability is present because you're going to fix it if it is. And two, you need a big, scary report to persuade your boss to spend more money. If neither is true, I'm going to save you a lot of money by giving you this free penetration test: You're vulnerable.

Now, go do something useful about it.

earlier essay: Privatizing the Police Puts Us at Greater Risk
later essay: Real-ID: Costs and Benefits
categories: Computer and Information Security
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Photo of Bruce Schneier by Per Ervland.

Schneier on Security is a personal website. Opinions expressed are not necessarily those of Co3 Systems, Inc..