It’s now been about a week since Equifax announced the record-breaking breach that affected 143 million Americans. We still don’t know enough — but a few details have begun to come out about the causes of the attack. It’s now being reported that Equifax’s woes stem from an unpatched vulnerability in Apache Struts that dates from March 2017, nearly two months before the breach began. This flaw, which allows remote command execution on affected servers, somehow allowed an attacker to gain access to a whopping amount of Equifax’s customer data.

While many people have criticized Equifax for its failure, I’ve noticed a number of tweets from information security professionals making the opposite case. Specifically, these folks point out that patching is hard. The gist of these points is that you can’t expect a major corporation to rapidly deploy something as complex as a major framework patch across their production systems. The stronger version of this point is that the people who expect fast patch turnaround have obviously never patched a production server.

I don’t dispute this point. It’s absolutely valid. My very simple point in this post is that it doesn’t matter. Excusing Equifax for their slow patching is both irrelevant and wrong. Worse: whatever the context, statements like this will almost certainly be used by Equifax to excuse their actions. This actively makes the world a worse place.

I don’t operate production systems, but I have helped to design a couple of them. So I understand something about the assumptions you make when building them.

If you’re designing a critical security system you have choices to make. You can build a system that provides defense-in-depth — i.e., that makes the assumption that individual components will fail and occasionally become insecure. Alternatively, you can choose to build systems that are fragile — that depend fundamentally on the correct operation of all components at all times. Both options are available to system designers, and making the decision is up to those designers; or just as accurately, the managers that approve their design.

The key point is that once you’ve baked this cake, you’d better be willing to eat it. If your system design assumes that application servers will not contain critical vulnerabilities — and you don’t have resilient systems in place to handle the possibility that they do — then you’ve implicitly made the decision that you’re never ever going to allow those vulnerabilities to fester. Once an in-the-wild vulnerability is detected in your system, you’d damn well better have a plan to patch, and patch quickly. That may involve automated testing. It may involve taking your systems down, or devoting enormous resources to monitoring activity. If you can’t do that, you’d better have an alternative. Running insecure is not an option.

So what would those systems look like? Among more advanced system designs I’ve begun to see a move towards encrypting back-end data. By itself this doesn’t do squat to protect systems like Equifax’s, because those systems are essentially “hot” databases that have to provide cleartext data to application servers — precisely the systems that Equifax’s attackers breached.

The common approach to dealing with this problem is twofold. First, you harden the cryptographic access control components that handle decryption and key management for the data — so that a breach in an application server doesn’t lead to the compromise of the access control gates. Second, you monitor, monitor, monitor. The sole advantage that encryption gives you here is that your gates for access control are now reduced to only the systems that manage encryption. Not your database. Not your web framework. Just a — hopefully — small and well-designed subsystem that monitors and grants access to each record. Everything else is monitoring.

Equifax claims to have resilient systems in place. Only time will tell if they looked like this. What seems certain is that whatever those systems are, they didn’t work. And given both the scope and scale of this breach, that’s a cake I’d prefer not to have to eat.