Security Implications of Agile vs Waterfall

Security Implications of Agile vs Waterfall
By Justin C Miller
Posted 9/1/2014


Projects are a necessity in the corporate world. They provide a means for justification and cost estimation. They give guidance and put standards around big changes. They ensure something is built to be efficient and beneficial and well tested. They provide a means to look back, reflect, and improve for the next time.

Two of the more common methodologies you'll find are Waterfall and Agile.

In waterfall you do things in sequence one after another such as requirements, design, development, testing, and release. In general you end up with large volumes of documentation and a lengthy but thorough process. There tends to also be the risk that you'll build something big only to find out when you pass it off that it's no longer what the business wanted.

In Agile you do all those things, but in small tiny waves. In general you end up with very little documentation but you see results almost immediately. You can eliminate the risk of big surprises because the business is involved during each of those tiny waves.

So, a question you might contemplate is in terms of IT Security, does it matter whether my company is using Agile or Waterfall?

I contend that YES, the choice your company makes for Project Methodology has big implications on your company's IT security. I'll skip the dance and games and get straight to the point ... Agile has become a necessity in the corporate world if you're hoping to ensure your environment is secure.

Agile builds your massively complex software in small tiny waves, perhaps 2-4 weeks at a time.
Here are 5 examples of why Agile promotes a more secure environment than Waterfall ever will ...
1.) In Agile there are fewer features built at a time thus it easier to test, and testing is an important step in finding security vulnerabilities. Imagine being asked to test whether the security groups are configured correctly in your application's 10 administrative screens, each of which have 50 tests cases each. Would you be more likely to get it right if you had to test one of the screens/50 test cases at a time, or if you had to test all 10 screens and 500 test cases at once ? Short and sweet means you can concentrate more and feel less stressed and time constrained and get it right.
2.) There are fewer lines of code to review at a time, thus the peer reviews of the code are going to be done more thoroughly and get a good solid look. I've seen it happen way too many times where in your waterfall project you just get done creating 100's of code files and 1000s of lines of code, and now your code review becomes weak and pathetic ... because you'll NEVER get a developer to review 100's of files and 1000s of lines of code in one shot. But in an Agile scenario it is much more realistic to expect them to view a handful of files and a few lines of code and review it correctly.
3.) One of the key aspects of IT security is code complexity. The simpler the code, the easier it is to secure, the easier it is to understand and the less likely it is to contain a mistake. Thus Agile brings big benefits again because you're writing smaller chunks of code that are less complex and thus by default easier to secure.
4.) Waterfall projects have a history of lasting months if not years from inception till completion. If you've been paying attention to the current state of IT security then you know that things change much quicker than that in our arena. Therefore if you start a project on a certain version of software using certain defense techniques, by the time the project is complete the vendor has probably released numerous software updates, security patches, and even the techniques used to prevent and mitigate vulnerabilities may have changed. Thus by the time a Waterfall project is deployed it's likely already old and out of date and needing an upgrade. Agile on the other hand is pushing out fixes every few weeks and by definition allowing for changing requirements, not just changing business requirements but also changing security requirements. If a patch or vulnerability needs a quick fix, you're able to toss it into the backlog as a feature on the next wave. With Waterfall you'll have a nightmare of a time trying to work it in, and things that get pushed to the backlog in Waterfall typically wait until the project is completely over. Too long in our world.
5.) The biggest, and perhaps least obvious advantage that Agile brings to the table over waterfall is a mindset. You go from moving slow, turning the Titanic, to moving swiftly, piece-mealing it to get the job done quickly. I've seen it many times already where those companies stuck in the mindset of Waterfall are the same companies that struggle to get security patching done because they want to plan it for a month, test it for another month or two, then deploy after a few weeks of Change Advisory board discussions. This of course leaves your company open and vulnerable while you're waiting for the process to play out. The Waterfall mindset also leads to end-of-life software hanging out there because the project is just too large and intense to upgrade ... which obviously is a huge security risk. The Waterfall mindset also leads to known risks being pushed off, delayed, or kicked down the road into the next project. That mindset is just not acceptable in this day and age.


IT projects are just like IT Security ... they're too big and complex to bite off in one chew. The only way you're going to succeed is to cut them up and tackle them as smaller pieces of the puzzle. Get your head wrapped around the idea that the IT world moves quickly and you have to choose a project methodology that matches that pace. Agile is the clear front runner of project methodologies when you're discussing the implications it makes to IT security.

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