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SAST vs. DAST for Security Testing – How do they differ?

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Application Security Testing (AST) encompasses various tools, processes, and approaches to scanning applications to uncover potential security issues. Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST) are popularly used security testing approaches that follow different methodologies of scanning application codes across different stages of a software development lifecycle.

SAST follows a white-box testing approach to analyze the source code, byte code, and binaries to identify exploitable vulnerabilities and coding errors. On the other hand, DAST implements a black-box testing method, where security engineers parse simulated attack payloads through the application’s front end without exposing internal information on the application’s internal construct. This article discusses SAST vs. DAST testing approaches, how they help detect vulnerabilities and application failures, their differences, and the most appropriate use cases.

DAST and SAST – Testing Mechanisms for Identifying Application Vulnerabilities

Static Application Security Testing (SAST) tools provide instant feedback on software flaws introduced in the code development process. The test is executed using predefined rules on a model of the software that combines its source code and data flows to create a replica. As the testing methodology is implemented since the early stages of a software development lifecycle, SAST helps identify coding errors before the software is compiled. As a result, SAST is a preferred testing methodology that supports a DevSecOps-based shift-left approach to administering security.  

Common security vulnerabilities uncovered by static application security testing include:

Benefits of SAST scans include:

  • Early vulnerability detection – Static Code Analysis is performed at the beginning of the development process, where the test helps detect errors within the application code before it is compiled. By ensuring that security flaws don’t make it into production, SAST tools help enforce proactive protection and mitigation of security flaws.
  • Real-time feedback – SAST scanners perform rapid scans and can analyze the entire code base of an application in a shorter duration. Apart from providing instant feedback on the uncovered flaws, SAST tools seamlessly integrate with various development pipeline tools without impacting core functionalities.
  • Accuracy – SAST tools perform security tests automatically based on predefined security rules. These tools identify critical vulnerabilities faster and more accurately than manual testing approaches.

While SAST aids a secure coding practice, the benefits of analyzing static code are limited in scope since it cannot identify runtime vulnerabilities and comes with a higher risk of reporting false positives.

Unlike SAST, Dynamic Application Security Testing evaluates the application using an outside-in approach by simulating the actions of a malicious user to orchestrate attacks. DAST scans operate by entering suspicious user inputs and observing the application’s response to evaluate runtime vulnerabilities. The testing mechanism continuously scans web applications deployed in production, helping simulate the application’s real-world behavior and identify issues affecting the typical user experience. Since DAST tests are performed in a runtime environment, security engineers can also detect and identify new vulnerabilities as they arise and evolve.

Application vulnerabilities uncovered by dynamic analysis of application code include:

Benefits of DAST tests include:

  • Language agnostic – DAST tests do not require knowledge of the programming languages used to develop the application. DAST tools evaluate the application’s behavior based on inputs and outputs no matter the frameworks used, making it a more robust testing approach. Since they are built to be language-agnostic, DAST tools enforce seamless collaboration between development and security teams for easier security risk management.
  • Low rates of false positives – DAST tools perform end-to-end scanning of the application environment, enabling security researchers to detect and identify security flaws that threaten the application’s security and functionality.
  • Does not require access to source code – As DAST scans are performed by sending malicious payloads through the application’s front end, enterprises can leverage third-party security services to perform tests without exposing the application code.

While DAST tools evaluate a wide range of vulnerabilities within the application code, they cannot detect the exact location of a security issue within the codebase. DAST scans also fail to sniff vulnerabilities in parts of the application stack that do not execute.

What is the difference between SAST and DAST?

While both DAST and SAST mechanisms follow a proactive vulnerability identification and risk management approach, they offer different strengths for varying use cases. The following section outlines the differences between the two technologies and the factors to consider when choosing the right application security tool.

DAST vs. SAST

The table below highlights the key differences between static and dynamic application security testing aspects.

AspectSASTDAST
Test TypeWhite-box testing methodBlack-box testing method
Code maturity requiredScans partial code at restScans mature, running code
Vulnerability coverageCoding errors and misconfigurationsRuntime vulnerabilities
Location of vulnerabilitiesFinds the exact locationIt only detects vulnerabilities but doesn’t pinpoint a particular line of code.
False positive reportingHigher rate of false positivesLow rate of false positives

When to Use a SAST Mechanism?

SAST is considered invaluable in modern software development life cycles as it helps detect and resolve critical vulnerabilities before they make it to the production environment. This is primarily because the cost to remediate vulnerabilities is the least at this stage of the SDLC.

As a best practice, SAST tools are recommended to be used by developers to help them identify and detect coding errors while they are writing the software. SAST is also appropriate for root cause analysis, which helps determine the exact location of the problem within lines of code after other vulnerability scans have detected flaws.

How to Combine SAST and DAST Mechanisms For Optimum Results?

Since they offer varying strengths, DAST and SAST complement each other and are best used together for implementing a much more robust testing approach. A practical method is to adopt SAST tools early in the code development stage, enabling comprehensive security analysis of all functionalities and packages used for the application. Then, the source code, binaries, and dependencies can further be loaded into a staging environment where security engineers can perform DAST tests to assess how attackers can exploit vulnerabilities in production.

The approach is different for instances where the application is already deployed in production. In such cases, DAST can be used to detect new or unknown vulnerabilities. In addition, SAST scans can be administered to vulnerable components to identify the root causes of a vulnerability.

Development teams use several tools collectively to reduce the burden of administering DAST and SAST tests. These tools operate on a set of security rules to automate the discovery, identification, and remediation of security vulnerabilities. 

Some popular SAST tools include:

OWASP ASST

OWASP Automated Software Security Toolkit (ASST) is an open-source toolkit that checks source code files line-by-line for misconfigurations and vulnerabilities. While the tool primarily focuses on web applications built with MySQL and PHP programming languages, it also supports plugins that add features and support for other application frameworks. If it detects a security risk, the toolkit reports the lines on which vulnerabilities were found and remediation options to harden security.

SecureAssist

A minimal static analysis tool that detects security misconfigurations and provides real-time hardening recommendations. Apart from supporting major frameworks, including .NET, PHP, JavaScript, and Java, SecureAssist also supports plugins for multiple Integrated Development Environments (IDEs), such as Eclipse, IntelliJ, and Visual Studio.

DeepSource

DeepSource is an easy-to-install static code analysis tool that continuously analyses code to detect and fix security issues and malicious code. The tool integrates seamlessly with GitHub to analyze every pull request to ensure only clean code is deployed to production. 

Some popular DAST tools include:

Nessus

Nessus is a penetration testing platform that primarily performs network scans to identify security vulnerabilities by testing against known vulnerabilities. The platform has a broad range of adoption, with over 2 million enterprises using it due to a low rate of false positives and the number of vulnerabilities covered.

OWASP ZAP

OWASP Zed Attack Proxy (ZAP) is an open-source security scanner that allows easy penetration testing to detect exploitable application vulnerabilities. OWASP ZAP is actively maintained by a dedicated international team of security professionals and volunteers, making it a tool of choice for experienced users who perform manual security scans.

Crashtest Security

Crashtest Security Suite is an automated penetration testing platform that helps reduce security risks in modern web applications and application interfaces. The platform is an online SaaS offering that helps save time and budget on threat modeling by automating tests and offering actionable reports on discovered vulnerabilities.

To know more about how Crashtest Security can help eliminate security blind spots, try a free 14-day trial here.

FAQs

What is the difference between SAST and Penetration Testing?

SAST is an application testing technique that scans application source code files for development errors. In addition to security, SAST helps to determine code quality, reusability, and maintainability.

On the other hand, penetration testing is a testing approach where security engineers mimic the actions of a malicious actor to assess how vulnerabilities are typically exploited. Unlike SAST, penetration testing covers a broader range of exposures and can be outsourced to contracted firms for niche expertise and an unbiased security review.

What are the types of SAST?

Depending on what is being tested, SAST testing can be categorized into:

  • Source Code Analysis
  • Byte Code Analysis
  • Raw Binary Code Analysis

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