Author Robert Collier said that "Success is the sum of small efforts repeated day in and day out." That's especially true when it comes to security. By now we all understand that securing your systems isn't as simple as installing a firewall and calling it a day. Instead, it's multiple actions and strategies in concert, implemented consistently over time. And believe it or not, one small but important strategy is simply writing code that's reliable (bug-free) and maintainable (easy to understand). Yes, I know that sounds too simple, and possibly even self-serving. So in this post, I'll lay out some of the evidence for how writing reliable and maintainable code means you're inherently writing more secure code.
Poor Maintainability Contributed To Heartbleed
To make the case for how maintainable code contributes to security, I'll start with the Heartbleed Bug. Remember that one? It was a serious vulnerability in OpenSSL that allowed attackers to steal sensitive information with a really trivial attack that XKCD illustrates beautifully. David A. Wheeler teaches a graduate course in secure development at George Mason University. He wrote an extensive analysis of the vulnerability. In it, he laid part of the blame on the difficulty of simply understanding the code involved: "Many of the static techniques for countering Heartbleed-like defects, including manual review, were thwarted because the OpenSSL code is just too complex. Code that is security-sensitive needs to be 'as simple as possible'."