DAST vs. Penetration Testing – What’s the Difference?

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Facing a data breach is a make-or-break moment for any business, whether big or small. For that reason, learning how to protect your information from threat actors is a must. To do so, you have to employ DAST and penetration testing, though they’re not the same. Here are the differences.

The main difference between DAST and penetration testing comes from who performs it: the first is done by software, while the latter is performed by a professional. DAST can run continuously without ever stopping, while pen testing is usually done two to four times per year.

Can DAST replace penetration testing since it can run forever and requires little oversight? If that’s true, should you ever call a pen tester to see how secure your system is? This article will show you the right direction when setting up your cybersecurity policy.

DAST vs. Penetration Testing: A Definition

Beginners usually confuse DAST and penetration testing because they seem similar when seen from afar. However, it’s critical to differentiate them if you want to do a thorough cybersecurity audit.

  • DAST. Dynamic Application Security Testing (or DAST for short) is an automated way to check for vulnerabilities in software or websites. However, more often than not, it’s used for web-related projects. When people talk about DAST, they often refer to DAST tools, which are software that helps users scan for possible vulnerabilities in code, such as the chance of an XSS attack taking place.
  • Penetration Testing. Penetration testing is an exhaustive process performed by a professional or team of professionals who assess the integrity of a system. A pen tester can check how secure a software, website, or company is. They can use every tool of the trade (including DAST itself) to check how secure the system they’re auditing is.

The Main Difference Between DAST and Penetration Testing

DAST is a software-based approach to auditing a system. It has no access to the source code and can only identify certain vulnerabilities. In contrast, penetration testing is a more thorough approach that may have access to the source code.

At the same time, a DAST scan’s scope is limited: it can only deal with software or websites, and it’s usually used for the latter. However, a company could hire a pen tester to see if their employees tend to fall for phishing attempts, which is one of the biggest reasons why data breaches happen (with ransomware being a close second).

Who is doing the testing matters too: since DAST is a software-based approach, users with little expertise can do it, considering software does the heavy lifting. However, a pen tester is usually a professional with years of experience, meaning hiring one has a higher chance of finding the vulnerabilities a DAST scan won’t expose.

Simply put, DAST is a surface-level scan that deals with plenty of vulnerabilities – but far from all. A pen test is a more thorough approach that could happen in multiple ways, including auditing your source code (which a DAST scan can’t do).

A Metaphor to Better Understand the Difference

Imagine you’re guarding a treasure inside a fortress. You haven’t built that fortress, nor have you tested it against invasions, so you get a little uneasy about possible threats. For that reason, you decide to go on the market to increase your security – but you don’t know where to start!

So, first, you hire someone to test things out: he’ll look at the fortress from the outside, pick the locks, kick the walls, and do a few more things to see if he can cause any damage, though he’ll always stay on the outside.

Every three to six months, a spymaster comes through and offers his services: he’ll try to sneak inside your fortress without anyone knowing, test the loyalty of your guards (to see if he can bribe his way in or steal any keys), and more. Of course, he’s more expensive – but more efficient as well. That’s a penetration tester.

There’s a third way of doing things (called Static Application Security Testing, or SAST for short) that is similar to DAST but different in scope: the first worker, instead of looking from afar, would have access to the schematics of your fortress. In other words, SAST can access your code, while DAST can’t.

How Does DAST Work?

A DAST tool will scan a website looking for vulnerabilities and report them if there are any. It won’t scan for vulnerabilities alone but actively try to inject malicious code into a website. Since it has no access to the source code, it’ll try every attack it has in its library. In a way, you could say it brute forces attacks to see what could happen.

However, no harm will be done to a website during this test. In fact, if you’re afraid of running a DAST scan, you’re going to do more harm than good. This type of work is necessary to rule out any zero-day vulnerabilities that could destroy the credibility of your product, force a massive recall, or put your software engineers on overdrive to release a patch.

Using a DAST scanner is simple: you download it, set it up, and let it work. You have to do very little to find vulnerabilities. However, this method is far from a magic fix, meaning you’ll need someone to do more extensive work if you want to thoroughly audit a system.

Why is DAST Needed?

DAST will deal with a lot of vulnerabilities that your software engineers may have overlooked during the production phase. In fact, this scan is very important when you have a final product in your hands that’s yet to be released to the public.

Running a DAST scan before your product reaches the masses is a great way to prevent dealing with releasing patches early on. At the same time, as you incorporate new code to update your product, you should continue to run DAST scans to see if something comes up.

Can you rely on DAST to find every vulnerability a product has? Not at all! You need to hire a pen tester to do a more thorough audit if you want to find every way a threat actor would harm your system.

In fact, DAST doesn’t deal with the human element (unlike pen testing), one of the biggest issues in cybersecurity.

How Does Pen Testing Work?

A pen tester will take a thorough look at your system to figure out how a threat actor would try to undermine its defenses. In other words, the perfect penetration tester would actively look for vulnerabilities and show you where the weaknesses are.

In a way, a pen tester is a hacker who doesn’t want to harm your system but help you improve it. For that to happen, they have to act as if they want to take total control over your system, software, company, or anything else you want to audit.

Penetration testing often takes place in five steps:

  • Plan. The first step is to study the system a pen tester will attack. Getting as much information as possible is the key to unlocking a successful attack. Doing so means learning about hardware, software, and the people involved.
  • Scan. Once the pen tester knows what they’re dealing with, they’ll actively look for open spots. In fact, it’s possible whoever is pen testing will use a DAST scan (among other tools) to look for vulnerabilities.
  • Assess. After the scan, the pen tester has a long list of vulnerabilities they can exploit. However, not every attempt is worth taking, as some would alert employees. Passing undetected is key for a pen tester.
  • Exploit. In this step, the attack takes place. It doesn’t happen at once. Throughout a day or a couple of days, the pen tester will take down a system’s defenses one by one and access critical data they shouldn’t have access to. If possible, they’ll remain inside the system for a while.
  • Report. A pen tester must write a thorough report explaining where the vulnerabilities are and how to fix them.

When Should Pen Testing Be Done?

Companies should hire pen testers to audit their system at least once a year, preferably two to four times per year. Technology evolves quickly, and threat actors take advantage of that and adapt, damaging those unwilling to do the same.

Unfortunately, penetration testing is far from affordable, forcing most companies to relegate or relinquish thorough cybersecurity. However, refusing to hire penetration testers to audit your product could be costlier than the test itself.

Bug bounty (pen testers looking for vulnerabilities) is a very lucrative industry for that reason. The biggest companies in the world pay millions of dollars to people who find zero-day vulnerabilities. However, these exploits are sold to honest companies and threat actors alike.

Is DAST Better Than Penetration Testing?

Not at all! Although these two approaches serve two different needs, you shouldn’t think DAST is better than pen testing. It’s more affordable and requires little knowledge to perform, but that comes with a cost: in contrast, pen testing is a more thorough audit.

In other words, penetration testing will deal with every element of cybersecurity. DAST only deals with a certain set of threats, which are dangerous – but far from the whole list of vulnerabilities that could pose a threat.

For example, DAST can find the possibility of an XSS attack taking place due to outdated or poorly-written code, and it could do so fast. A pen tester could also find it, and it could also find out whether users and employees are susceptible to phishing attempts, among other things.

One of the biggest issues with DAST is that it never deals with source code. While that’s necessary (because this scan performs black box audits to emulate a threat actor’s behavior), it means you’ll never find design issues this way.

Can DAST Replace Pen Testing?

DAST cannot replace penetration testing. Doing a DAST scan will feel like a surface-level approach when you compare it to a thorough pen test. That doesn’t mean you should forget about DAST since we’re talking about a great tool you must use.

You could interpret DAST as quality control. You use it before you launch a product and after launching it, so you can make sure threat actors can’t take advantage of any vulnerabilities. Doing constant checks reduces the chance of missing out on anything.

Regular scans would be akin to car maintenance work: you can check if your tires have enough air pressure, the lights work properly, and the oil is okay. Anything more serious requires the help of a trained professional.

Pen testing is like taking your car to the shop: a professional can do a thorough check and deal with anything under the hood you don’t understand. Sure, you can check the oil, but a veteran in the field will know if something is wrong with your engine.

Can Pen Testing Replace DAST?

Penetration testing can replace DAST – but not in the way you think. Big companies (especially those that specialize in tech) have in-house cybersecurity analysts who take the role of pen testers around the clock. However, that doesn’t mean they stop running DAST.

As you now know, anyone with little expertise can fire up DAST software and check for vulnerabilities. Small businesses rely on that to avoid making huge mistakes when it comes to security. 

Hiring an in-house pen tester wouldn’t stop you from running DAST; instead, the pen tester would take care of it.

Since a professional penetration tester would be running DAST, he’d use it along with other tools in his arsenal to better improve your security.

Conclusion

You should continue running DAST and use it as your first line of defense. However, regular penetration testing should be mandatory if you want to take cybersecurity matters seriously. These two practices complement each other, meaning neither can replace the other.

Herman

Herman McCargo is a Cyber Defense Analyst here at U.S. Cybersecurity. He’s been in the technology field for over 20 years and has expertise working with the most critical technology infrastructures. He has a deep understanding of cyber risks, threat mitigation and prevention, and overseeing infrastructure.