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SAST vs. DAST: A Detailed Comparison

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2023 research by Statista reports that over 3,000 data breaches occurred that year alone. As security threats increase, development teams must find innovative ways to improve their application security testing. Two key methods are Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST).

SAST scans the application source code to identify security vulnerabilities, while DAST tests the running application from the outside in to check for vulnerabilities. Both techniques have advantages and disadvantages, and they are best used in conjunction to provide a robust security posture.

In this article, we'll define SAST and DAST, explore their differences, and discuss how to use them in real-life scenarios for maximum effectiveness. Understanding these two testing methodologies allows you to make informed decisions and implement a comprehensive application security testing strategy to safeguard your applications.

What is SAST (Static Application Security Testing)? 

SAST, or Static Application Security Testing, is a type of security testing that analyzes the application’s source code in a static or non-running state to identify security vulnerabilities. This testing method is often called “white box” because it analyzes an application's internal state (source code).

SAST is typically performed during the early stages of the software development lifecycle (SDLC), such as code development or code review phases. Its primary goal is to detect issues like SQL injection, cross-site scripting (XSS), hardcoded credentials, and other OWASP Top 10 vulnerabilities directly within the code.

While SAST helps identify potential security vulnerabilities, it has challenges. One key limitation of SAST is its inability to detect runtime or environment-specific vulnerabilities, such as configuration errors or issues related to runtime dependencies.

What is DAST (Dynamic Application Security Testing)? 

Dynamic Application Security Testing (DAST) is a security testing methodology that assesses an application while it’s running. Unlike SAST, which focuses on the code itself, DAST interacts with the application as an external user (like a “black box”), sending requests and analyzing responses to identify vulnerabilities. DAST is typically performed in later stages of the SDLC, such as during integration testing or pre-deployment phases.

DAST detects vulnerabilities in web servers, databases, and other application services, such as authentication flaws, session management issues, and misconfigurations. This testing approach provides a real-world perspective on an application's security posture, simulating how attackers might exploit vulnerabilities in a live environment.

SAST vs. DAST Tools: What Are the Differences?

The main differences between SAST and DAST lie in their testing approach and the stage in which they are run. Here's a more detailed comparison:

 

 

SAST 

DAST 

What They Scan

Scans the source code of an application to identify vulnerabilities and security issues

Scans running applications and APIs (such as REST, GraphQL, and SOAP) that your application connects to, testing them from an external perspective

When They Scan

Occurs early in the software development lifecycle, shortly after the code is written

Happens later in the SDLC once a working application is ready to run in a test environment

Testing Approach

Uses white-box testing to look for vulnerabilities inside the application and code

Uses black-box testing to search for vulnerabilities that could allow an outside attacker to gain access

Language Dependence

Implementation depends on the programming languages and development frameworks used in the application and the specific SAST tool being used

Is language-independent, as it tests the application from the outside, regardless of the underlying technologies used

SAST vs. DAST: Weighing the Pros and Cons

While SAST and DAST offer valuable security assessments, each approach has strengths and weaknesses. Understanding these differences can help you determine which method (ideally, a combination of both) best suits your development process.

SAST Pros

  • Early Integration: SAST shines in its ability to be integrated into the earliest stages of development. By identifying potential vulnerabilities early in the development lifecycle, SAST allows developers to address them promptly, often while the code is fresh in their minds. This reduces the time and effort required to fix issues compared to waiting until later stages when the code becomes more complex.

  • Precision: SAST can pinpoint the exact location of a vulnerability, including file name and line number, making it easier to resolve a vulnerability.

SAST Cons

  • False Positives/Negatives: SAST analyzes code snippets in isolation without considering the broader application logic or how different parts of the code interact. This can lead to scenarios where a code pattern might appear suspicious but is used safely with proper sanitization or validation in the actual application.

  • Language Dependence: SAST tools are designed to understand the syntax and constructs specific to the programming languages they support. Each language has its unique way of handling data types, string manipulation, and memory management.

  • Static Analysis Limitations: SAST tools analyze the code without executing it, which means they can miss vulnerabilities that only manifest during runtime. For example, SAST tools might not detect issues related to dynamic code execution, complex object interactions, or specific runtime conditions. 

If you're using a programming language that the chosen SAST tool doesn't support, the tool might be unable to analyze the code for vulnerabilities effectively. This can leave significant portions of your application untested, potentially creating security gaps.

DAST Pros

  • Real-World Perspective: DAST tests the application from an external user's perspective, simulating an attacker's approach. This allows it to identify vulnerabilities that may only manifest during runtime, such as misconfiguration issues or vulnerabilities in the application's interactions with its environment.

  • Comprehensive Testing: DAST can test the entire application environment, including APIs and web services, providing a more holistic view of the application's security posture.

  • Programming Language Agnostic: DAST does not require access to the application's source code, making it suitable for testing applications built with various technologies and frameworks.

DAST Cons

  • Later Stage Integration:  DAST is typically used later in the development lifecycle, as it requires testing a working application. This means that vulnerabilities found by DAST may be more expensive to fix than those identified earlier in the process by SAST.

  • Configuration Complexity: Effective DAST scans require configuration specific to your environment, potentially demanding expertise in penetration testing techniques.

  • Lack of Source Code Visibility: Unlike SAST, DAST cannot directly show the exact lines of code where vulnerabilities exist. It provides insights into runtime behaviors and potential attack vectors but may not offer the same level of granularity in pinpointing vulnerabilities within the source code.

When To Use SAST vs. DAST: Real-world Scenarios

Understanding when to use SAST and DAST optimizes your application security testing strategy by addressing vulnerabilities across various development stages. Here’s where each of them should be used.

SAST 

  1. Early Development Phases: SAST can catch common vulnerabilities such as SQL injection or Cross-Site Scripting (XSS) early in the development cycle when they're easier and cheaper to fix.

Code Example (Java):

String userInput = getUserInput(); // Get user input from a form
String query = "SELECT * FROM Users WHERE username='" + userInput + "'";
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(query);

The SAST tool flags the concatenation of user input directly into the SQL query, highlighting the vulnerability.

  1. Code Reviews: SAST's ability to pinpoint vulnerabilities in the source code is crucial for improving code reviews. SAST can scan the code before it's committed to the main repository, allowing developers to review their code before being checked into the main codebase.

Code Example (Javascript):

  1. Pre-Commit Hook: A SAST tool is integrated into the version control system as a pre-commit hook.

  2. Code Submission: A developer attempts to commit code.

  3. SAST Scan: The SAST tool scans the code and identifies a potential XSS vulnerability.

  4. Review and Fix: The developer reviews the flagged code and sanitizes the user input.
// Original code
document.getElementById('output').innerHTML = userInput;

// Fixed code
document.getElementById('output').innerText = userInput;

DAST 

  1. Pre-Production Testing: DAST can uncover issues such as database misconfigurations, insufficient authentication mechanisms, or insecure direct object references (IDOR) that may not be apparent in static code analysis.

  2. Third-Party Integration Checks: DAST's external perspective mimics an attacker's approach, making it suitable for identifying vulnerabilities in interconnected systems. DAST can reveal issues such as insecure API endpoints, data leakage through APIs, or insufficient access controls in external services.

Here’s how a DAST tool works in a typical coding environment.

  1. The application is deployed to a staging environment.

  2. A DAST tool scans the running application and simulates various attacks.

  3. The tool identifies an IDOR vulnerability where users can access other users' data by modifying the URL.

  4. Developers implement proper access controls to ensure users can only access their own data.

Combine SAST and DAST for an Effective Application Security Program

By combining SAST and DAST testing, you can create a multi-layered security testing strategy that addresses vulnerabilities at both the static code and runtime environment levels, providing a more holistic view of your application's security posture. Automating SAST and DAST scans with Continuous Integration and Continuous Deployment (CI/CD) allows you to accelerate development time without sacrificing your application’s security.

Codacy's security features provide static analysis for a wide array of programming languages, automated security scanning, and AI-powered real-time insights, helping you shift security left and address vulnerabilities early. Start your free trial today.

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