SAST vs DAST: A Comprehensive Guide (2021)


Application Security: Not a buzzword that you hear a lot, do you? Well, you are right. It is not the type of testing that makes the headlines too often; nonetheless, it is an important feature of applications that are in the public domain. So, what is Application Security?

Application security explores vulnerabilities at the application level aiming to keep the data and code used within the app safe from the external environment, ensuring that the application is failsafe against hacking attempts. A simple example is how an application collects and stores login credentials. You don’t want an application to deal with this important feature in a naïve way, like storing the usernames and passwords in a database without any kind of sane protection. Application Security deals with the security considerations during all phases of the development of the application.

Application Security Testing is putting your application to the test on various parameters that application security seeks to ring-fence and make airtight. 

  1. How important is application security testing?
  2. Static Application Security Testing (SAST)
  3. Dynamic Application Security Testing (DAST)
  4. Difference Between SAST vs DAST

1) How important is application security testing?

You should ask this question, Adobe. Adobe found the answer to this question the hard way in 2013 when hackers gained access to usernames, email addresses, credit card details, and more. It was found later that the encryption used by Adobe was suspect. In software testing, application security testing should be taken seriously. Adobe scraped through that disaster; not every business will.

There are two schools of testing Static Testing and Dynamic Testing. Static Testing involves examining all aspects of application development without any compulsion to see the application in action or the running interface; in other words, this kind of testing does not look at application behaviour. The whole point is to not wait until an executable product is ready. Errors are detected in the early stages of development. Dynamic Testing is more of a black box testing technique, where every attempt is made to break into an application from the outside. Testing here deals with the application execution, its behaviour, the interface it presents. It is done to simulate hacking and try and figure out any vulnerabilities.

Now when these concepts are stretched over to the application security domain, and we get 

Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST).

 So, which one is the best one to go with, SAST vs DAST? Tough one to answer right away. Let’s look at the strengths and weaknesses of each and then maybe you can make a decision yourself. 

2) Static Application Security Testing (SAST)

Static Application Security Testing seeks to find out vulnerabilities or security holes within the application early on in the development life cycle. This is very much in contrast to the Dynamic version, which requires a fully functional and ready product to start testing. In other words, SAST is white box testing, and DAST is black-box testing.  So why SAST, you may ask? Well, SAST goes beyond what is visible of the application to the user; it goes beyond the interface it displays. SAST involves putting the code through rigorous checks that could lead to a security breach in the product down the line.  A SAST can pull up issues in the code that exhibit anomalies like

  • Uninitialized variable, holding an undefined value,
  • Lack of consistent interfaces across modules
  • Unused variables
  • Code that never gets executed
  • Violation of standard programming practices
  • Security vulnerabilities 

and more.

3) Dynamic Application Security Testing (DAST)

Dynamic Application Security Testing, on the other hand, is a black-box testing technique, where the test has visibility of the application’s interface alone. Attempts are made to break the application into leaking information like usernames and passwords, bank account details and other valuable information. It is akin to asking a hacker to hack your application and point out any vulnerabilities. Dynamic testing works with software that is executable, that has a ready user interface which can be tinkered with by a hacker. Most common vulnerabilities found during such testing are,

  • SQL injection
  • Cross-site scripting
  • Memory corruption
  • PHP injection
  • JavaScript injection

and more.

4) Difference Between SAST vs DAST

Given below are head-to-head differences between SAST vs DAST.

SAST is a White Box testing technique, where it is essential that the code, system requirements, documentation are all available. DAST is a Black Box testing technique, where it is essential that a working application is available. Ideally, a full-featured application, but sometimes a working prototype might work to test a prototype.
SAST, if done well, will help you plug security holes as you keep developing your application.  DAST can only figure out a vulnerability once a working prototype or full-featured application is ready to be executed
You need application testing personnel skilled in the programming language used to develop the application, programming methodologies, well versed in software development methodologies, operating system functioning, memory management, database technologies, among other skills—basically, a full stack developer who knows principles of testing and the application security fundamentals. You won’t need a full stack developer here, but you do need a certain skill in understanding and manipulating various parameters that the application runs on to be able to try and break the system—basically, an application or system or network hacker, or a combination of all the 3.
Testing here requires access to source code. Testing here requires access to an executable form of an application, some form of interface that the tester can use. Ideally, a fully developed application.
Although SAST can pre-empt errors by looking through the code structure, but cannot really pre-empt runtime anomalies that are not apparent from the code. DAST will be able to capture any runtime anomaly as it attempts to run the application in every possible way to induce a breach.
The cost of fixing errors is very low in SAST as the errors or security holes are detected during the development phase. The cost of fixing errors after the application is built is always high and much more time-consuming.


Now that you have a fair idea about the differences of each, you get to chose what is the best type of application security testing for your application software. As a rule of thumb, an upfront investment in SAST and a thorough one at that seems a prudent decision than suffering losses after the application is in the market and lose potential business. Remember, if it is an application that deals with personally identifiable user information and your public domain footprint are large, it is wise to run your application through SAST.

So, have you made up your mind to make a career in Cyber Security? Visit our Master Certificate in Cyber Security (Red Team) for further help. It is the first program in offensive technologies in India and allows learners to practice in a real-time simulated ecosystem, that will give them an edge in this competitive world.


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