Running a modern SaaS company involves more than just building and releasing software. The responsibility of protecting your customers’ personal data means you need to be relentless about developing trustworthy applications that not only deliver what they promise, but are robust, secure, and reliable.

In the cybersecurity space, two important terms you should be aware of are SAST (Static Application Security Testing) and DAST (Dynamic Application Security Testing). Both are tools for testing and improving your application’s security, but as they differ in timing and approach, they each have a unique impact on your software product.

We’ll explore the differences between SAST and DAST in more depth, but if you’re here for the TL;DR:

SAST - examines your application’s codebase early in the development cycle, looking for vulnerabilities during pre-production. Think of SAST as having an engineer review your architect’s blueprints for that new house build.

DAST - examines your application in its operational runtime environment, looking for vulnerabilities post-development. Think of DAST as a security inspector attempting to breach your home’s security measures, trying to gain access from the outside after the house has been built.

A comprehensive strategy wouldn’t be complete without either method, as each plays a vital role in maintaining tight software application security.

What is SAST?

Static Application Security Testing is a method of ‘white-box’ testing that happens early in the development cycle, during which the source code and architecture of your software are inspected and analysed for vulnerabilities (at rest, without the application running).

Using our earlier house construction analogy, SAST helps ensure that the foundation and structure of the building are theoretically sound before the build commences.

SAST strengths include:

• Code visibility: with access to the source code, SAST tools have excellent (complete or near-complete) codebase coverage

• Time savings: automated SAST makes for quick identification of possible vulnerabilities across the codebase

• Cost savings: SAST tools help identify security flaws early, when they’re much cheaper and easier to fix

SAST weaknesses include:

• False positives/negatives: such comprehensive codebase coverage can often mean SAST tools return a high number of false positives (flagging a vulnerability that isn’t there) and/or false negatives (missing a vulnerability that is there)

• Lack of context: since the analysis happens pre-production on static code, your application’s runtime environment and other contextual factors aren’t accounted for

• Code availability: SAST tools are dependent on access to the source code, leading to possible blind spots in the case of third-party plugins or other external code

What is DAST?

Dynamic Application Security Testing is known as a type of ‘black-box’ testing, where the finished application sustains simulated real-world attacks within the context of its working runtime environment.

So once our house has been built, DAST helps verify that its defences are sufficient to repel intruders and withstand a variety of outside attacks.

DAST strengths include:

• Comprehensive: by testing the application in real-world scenarios, DAST provides a high-level overview of your software’s security health from the external perspective.

• Contextual: DAST takes into account the runtime environment and exposes your application to the kind of external threats it will actually face, making for a more robust, resilient application

• Language agnostic: unlike SAST, DAST is independent of your programming language, so there’s no need to configure or support internal technology variants

DAST weaknesses include:

• False positives/negatives: like its SAST cousin, DAST can also return false positives (flagging a vulnerability that isn’t there) or negatives (missing a vulnerability that is there)

• Timing: with DAST happening later in the development cycle, security holes aren’t uncovered until the product is live (or close to it). This can potentially increase the cost and/or difficulty of remediation

SAST vs DAST: the human element

Whilst there are automated security testing tools out there which can (theoretically) be run by the layperson, experience tells us they often end up being a false economy.

As noted for both SAST and DAST, the appearance of false positives can make it tricky to separate the wheat from the chaff. To the untrained eye, weeding these out can be laborious, slowing development as engineers spend time chasing would-be bugs in the code base, or investigating runtime security flaws that would never actually eventuate in a real-world scenario.

This is why it’s best practice to fortify your SAST and DAST with genuine security expertise. Automated testing tools are most powerful under the trained eyes of an expert. A skilled tester will interact with your application, adjust inputs and parameters to fit the environment, then properly interpret the results. Skilled professional ‘hackers’ can simulate real-world attacks on finished applications, delivering far better outcomes than automated tools alone.

In fact, when it comes to application security testing, we think human involvement is so important we built our company around it.

SAST vs DAST: which should you choose?

In the world of software security, it’s really not an either/or proposition. While every business has its own priorities and needs, a truly complete security solution involves a little of column S(AST) and a little of column D(AST).

Whether performed in a continuous integration (CI) pipeline or employed as part of a larger security project, SAST and DAST can (and should) be used together to better strengthen your security posture.

But if your business isn’t quite ready to dive headlong into the full suite of security testing tools, where should you start? Well, first consider the nature of your business, your software, and your team. Is there a recurring issue with code quality? Do you already have a robust Software Development Life Cycle (SDLC)? Or is your live application the main area of concern?

Evaluating your current security landscape and identifying the most pressing gaps will help you determine the best place to start.

If you need help implementing and managing DAST in your organisation, we can help. Contact us for a demo and get our expert team of hackers on your side.