DAST v. SAST: Which one is better?

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30 May, 2019

DAST v. SAST: Which one is better?

Earlier, security and privacy concerns were often used to be after-development activities, or they were ignored altogether. The ever-evolving threat landscape has definitely changed this position taken by the organizations and now, they are indeed concerned about the security issues associated with their application or software being developed. Or in other words, organizations are now ready to identify vulnerabilities in their products by themselves before they are exploited by an attacker.

In order to perform security testing, one will find two different strategies – dynamic application security testing (DAST), and static application security testing (SAST). Both of these methodologies assist an organization in finding vulnerabilities in their application so that chances of an information security incident are minimized.

SAST v. DAST – Differences 

The differences pertaining to SAST and DAST with respect to various parameters are shown in the table given below. 

  SAST  DAST 
Type  White box security testing  Black box security testing 
Tester’s Knowledge  A tester has complete access to the underlying architecture, including framework, design, algorithm, implementation, etc. of an application, and it is tested inside out.   A tester has no knowledge about the underlying architecture of an application, and it is tested outside in. 
Approach  Like a developer  Like a real-life attacker 
Requirement  SAST requires the source code of the application to be tested. It analyzes source code/binary without actually executing the application.  DAST requires a running application. It does not need to execute source code or binary. 
SDLC  It finds vulnerabilities in the earlier stages of a software development lifecycle, i.e., as soon as the code is deemed to have all the required features.  It finds vulnerabilities in the later stages of a software development lifecycle or at times; it often finds vulnerabilities after an application is deployed and a lifecycle is completed. 
Cost-factor  Since the vulnerabilities are found when a code is being developed, it is easier to fix them and incorporate the changes before the code is sent for a Quality Assessment.  Since the vulnerabilities are found in the later stages of a cycle, the updates are often considered for fixing in the next cycle. Critical updates may be undertaken as an emergency release. 
Run-time issues  As a SAST tool scans static code, run-time vulnerabilities are beyond its scope.  A DAST tool is capable of performing dynamic analysis on an application and is able to find run-time issues in an application. 
Scope  As a matter of general practice, SAST can be utilized for any type of software, including web application, mobile application, web services, etc.  Typically, DAST tools are platform specific. 

Which one is right for your organization? 

Our experts are often asked this question by our clients as to which of these methodologies is right for their organization. Here, it must be understood that either of these methodologies is not an alternative for another. Both these technologies work in tandem and they must be performed together to get the best possible results. For example, SAST finds errors in coding, while DAST finds runtime errors. Even though SAST tools generate relatively higher number of false positives, they are still quite popular among the development teams as they can find the flaws and write lines of code simultaneously. DAST, on the other hand, determines whether or not a function call is behaving as it should be.   

Lately, a term – Interactive Application Security Testing (IAST) – has emerged which combines essential elements of both DAST as well as SAST in order to address their shortcomings effectively. We will be exploring IAST in the upcoming articles. Meanwhile, do check out 3 Opensource Tools for DAST.