SAST vs. DAST: A Comparative Analysis

What is Static Application Security Testing (SAST)?

Static Application Security Testing (SAST) scans for compiled or non-compiled source code to identify vulnerabilities within that source code. SAST scanning analyzes an application’s source code, bytecode, or binaries without executing the application code or having any of the context of the runtime environment. SAST scanning is performed early, or “left,” in the software development lifecycle (SDLC), typically in the CI/CD pipeline, on code push, or using an IDE plugin. 

What is Dynamic Application Security Testing (DAST)?

Dynamic Application Security Testing (DAST) identifies vulnerabilities in a running application by simulating external attacks. DAST scanning does not require access to the source code. Rather, it tests the deployed application by simulating an attacker. DAST scanners are purpose built to interact with a live system – e.g. a development environment, staging environment, or (ideally not) production.

Key Implementation Differences Between SAST and DAST 

As a starting point, Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST) are not competitive. These scanning methodologies are actually quite complementary, but they do have inherent differences, advantages, and disadvantages. 

Differences in SAST and DAST Deployments 

The developer encounters risks at different points in the development lifecycle – such as an OWASP Top 10 vulnerability like an injection flaw – SAST and DAST are two scanning technologies that aim to address these risks at different points in the development process.

SAST scanning tools operate on the left of the software development lifecycle, in the CI/CD pipeline, within an IDE plugin, or on code push events. Developers get feedback from SAST scans, ideally, with clear attribution of where the detected risk exists within the source code. All SAST scanners are further left than DAST scanners but the level of context and actionability you get from a SAST tool can vary significantly based on where in the development lifecycle the SAST scanner is deployed. 

DAST scanners look for risks further “right” in the software development lifecycle, once the product is deployable. DAST tools tend to be more difficult to set up than SAST because DAST has to be configured to run against a specific environment with specific settings, such as credentials and specific recorded workflows. Additionally, DAST scanners do not have visibility into the context of the source code and are configured for a specific purpose. For example, if you configure a DAST scan based on authentication to a given service, you’ll get a specific result versus a different result if you run the same scan without authentication. While DAST scanners do not have the source code context, due to their deployment, they do typically have fewer false positive findings, assuming a standard tech stack. 

Again, because SAST scanners are looking at pre-deployment code and DAST scanners are looking at deployed code, these two scanning methodologies can be viewed as complementary. 

Scope of Testing & Types of Vulnerabilities Detected

Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST) do have an amount of overlap in what types of risks they can detect, but there are also risks that can be detected by one or the other. 

1. Risks Only SAST Can Find:

SAST scanners analyze an application’s internal code structure and can find vulnerabilities that arise from hardcoded secrets, poor coding practices, basic logic flaws, or configuration errors embedded within the source code. Since SAST examines the static code without running the application, it excels at finding code-related issues that don’t show up at runtime. Here are vulnerabilities typically found only by SAST:

• Unsafe or insecure coding patterns: Hardcoded secrets, credentials, API keys.
• Data flow issues: Mismanagement of data, such as improper validation, encoding, or handling of sensitive data in code.
• Insecure object references: Unsafe use of user-provided data in object instantiation or internal application logic.
• Unvalidated input from user-supplied data: Data taint analysis can detect where unvalidated input could traverse through code and cause security risks.
• Memory leaks and unsafe memory usage: Detects buffer overflows, memory mismanagement (particularly in C/C++ applications).
• Error handling flaws: Code that improperly handles exceptions or fails to handle errors securely.
• Misuse of cryptography: Incorrect implementation or usage of cryptographic functions (e.g., weak encryption algorithms, incorrect key management).

2. Risks Only DAST Can Find:

DAST is designed to assess the running application from an attacker’s perspective, so it finds vulnerabilities that manifest in runtime environments and that are not detectable by analyzing the code itself. These detected risks are often related to improper configurations or misbehavior under real-world usage. Here are vulnerabilities typically found only by DAST:

• Server and runtime configuration issues: Misconfigured HTTP headers (e.g., missing X-Content-Type-Options, X-XSS-Protection), improper security configurations (e.g., directory listings, exposed stack traces).
• Authentication and session management flaws: Weaknesses in how the application manages user sessions, including session fixation, session hijacking, and improper session termination.
• Unvalidated redirects and forwards: The ability for an attacker to redirect users to malicious sites using poorly implemented redirects.
• Information disclosure: Sensitive information leakage through error messages, server response codes, and HTML comments that can be used by attackers.
• Improper input validation at runtime: Though SAST can find input validation issues in the code, DAST can find these at runtime where certain user inputs might not be properly handled by the application, leading to injection attacks.
• Content security policy (CSP) weaknesses: CSP is evaluated in a live environment to ensure it effectively prevents malicious script execution.
• API vulnerabilities: Issues with improperly secured APIs, including misconfigured authentication, lack of rate limiting, and weak authorization mechanisms.
• Prompt injection attacks: Similar to API vulnerabilities, with the intention of identifying data leaks and code execution for LLM based services
• Business logic flaws: Issues where the application behaves incorrectly under specific conditions, like broken workflows, insufficient checks, or unintentional privilege escalation.

3. Vulnerabilities Both SAST and DAST Can Find:

Some vulnerabilities can be detected by both SAST and DAST but from different perspectives. SAST finds these by analyzing code patterns, while DAST detects them by interacting with the running application. Examples include:

• SQL Injection: SAST finds the flaw in how SQL queries are constructed, while DAST exploits it in the running application to confirm it exists.
• Cross-site scripting (XSS): SAST identifies potential XSS vulnerabilities in the code, while DAST tests how inputs are reflected in the output to confirm exploitation.
• Command Injection: SAST detects insecure code where user inputs could be used to execute system commands, while DAST attempts to execute these commands during runtime.
• Cross-site request forgery (CSRF): If the application lacks proper CSRF tokens or allows unauthorized actions via forged requests.
• Path Traversal: SAST identifies the code where improper validation allows directory traversal, while DAST tests if accessing sensitive files is possible via crafted URLs.
• Unvalidated input fields: Both tools can detect improper validation, though SAST does this by analyzing data flows in the code, and DAST finds these by injecting malformed inputs during testing.
• Insecure file uploads: SAST identifies insecure handling of uploaded files in the code, and DAST tests whether files can be uploaded and executed as attacks (e.g., uploading a malicious script).

SAST vs DAST: Cost-Benefit Considerations

While SAST and DAST scanning are complimentary, there is a significant premium placed on SAST findings because they are detected earlier in the software development lifecycle, and thus can be fixed earlier and with lower effort and human cost. 

With DAST scanning, a detected risk is already built and deployed. This means that when you fix a risk detected by your DAST scanner, you need to redeploy and retest in order to validate that the risk has been mitigated. 

SAST risks are detected further left in the development lifecycle and so the cost to fix is lower. That said, not all SAST deployments result in the same “cost” efficiency in mitigating risks. For example, if your SAST scanners are deployed in the CI/CD pipeline, and a detected critical SAST risk breaks your build, the effort involved in fixing can be quite high. SAST risks detected by an IDE plugin are detected much earlier and thus easier to fix, but because the count of results can be overwhelming, prioritization can be difficult and thus also can require significant effort. A SAST deployment that’s plugged directly into the source code – what we at Arnica call the “Pipelineless” approach – provides high cost efficiency because you can alert developers when a truly critical risk is detected before it goes to build, while providing rich context or even a recommended fix based on that context. 

Other Types of Application Security Testing (IAST, RASP)

While SAST & DAST have demanded the most attention recently in the world of application security testing, there are a number of other security testing methodologies that should be explored. 

Interactive Application Security Testing (IAST)

Interactive Application Security Testing (IAST) is essentially a more advanced DAST scanner. IAST can connect to the memory of the system it is testing against and can inspect in what is essentially a debug mode. The IAST scanner can then identify how that system reacts in the backend, which means fewer calls are required to determine if an attack exists. 

Runtime Application Self-Protection (RASP)

Runtime Application Self-Protection (RASP) is widely anticipated to be the next web application firewall (WAF) and, similar to a WAF, functions as an agent on your own software. When your RASP identifies a potential attack, it is able to block this attack at runtime. Some RASPs can be implemented with a prevention capability as well. 

Conclusion: SAST vs. DAST Comparative Analysis

Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST) represent distinct, complementary tools in the AppSec tool box. SAST helps identify vulnerabilities early in the software development lifecycle (SDLC), whereas DAST analyzes running applications. When used together, these two technologies provide effective coverage across the development lifecycle. 

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