SAST vs DAST vs SCA: Which Security Test Do You Need at Each Stage of Development?

Three testing methods form the core of modern application security: 

• SAST (Static Application Security Testing), 

• DAST (Dynamic Application Security Testing), 

• and SCA (Software Composition Analysis). 

They are complementary, not interchangeable — each catches a different class of defect, at a different stage, with different trade-offs. Running only one of them is… a blind spot.

 

SAST: Finding Flaws in Code Before It Runs

What it does

Analyzes source code, bytecode, or binaries without executing the application. Looks for patterns that indicate security weaknesses: SQL injections, cross-site scripting, buffer overflows, hardcoded credentials, insecure cryptographic usage.

 

When to run it

During development, as part of every commit or pull request. SAST is a code-time tool — it runs against the source as soon as the developer pushes it. In mature DevSecOps setups, SAST runs as a parallel CI stage alongside the build, delivering findings to the developer’s IDE or dashboard without blocking the pipeline.

 

What it catches that others don’t

Code-level logic flaws that only exist in the source — things like an insecure direct object reference that a functional test would never trigger. SAST can trace data flow through the application and flag patterns where untrusted input reaches a sensitive sink.

 

Limitation

SAST cannot see runtime behavior. It also generates false positives when it cannot fully resolve data flow, which is why AI-assisted triage — like DerScanner’s DerTriage, which filters up to 95% of false positives — materially changes the usefulness of SAST results.

 

 

DAST: Testing the Running Application Like an Attacker

What it does

Sends requests to a running application and analyzes the responses for signs of vulnerability. DAST operates as a black box — it does not see the source code. It tests the application the way an external attacker would: probing endpoints, submitting malicious payloads, and observing whether the application responds in ways that indicate SQL injection, XSS, authentication bypass, or security misconfiguration.

 

When to run

After deployment to a staging or pre-production environment. DAST requires a live, running application, so it cannot run during the build phase. The common pattern is to trigger DAST scans automatically after deployment to staging, with lightweight “smoke” scans on every deployment and full deep scans on release candidates or nightly builds.

 

What it catches that others don’t

Runtime and environment-specific issues that only appear when the application is fully assembled: misconfigured CORS, exposed admin endpoints, authentication flaws in the deployed configuration, and — critically — API authorization failures like the BOLA vulnerability that led to the HackerOne/Navia breach. If Navia had run DAST against its API, that vulnerability would have been detected.

 

Limitation

DAST cannot identify the root cause in source code, and full scans can be time-consuming. It also cannot test code paths that are not reachable from the application’s external interface.

 

 

SCA: Securing What You Didn’t Write

What it does

Identifies all open-source and third-party components in your application, checks them against vulnerability databases, evaluates license compliance, and — in modern implementations — assesses supply chain risk through package reputation and provenance analysis.

 

When to run it

On every build, continuously. SCA resolves the dependency tree at build time and checks it against known vulnerabilities. Because new CVEs are published daily, a project that was clean yesterday may have findings today. The September 2025 npm compromise (chalk, debug, 2.6 billion weekly downloads) demonstrated that organizations running SCA on every build caught the malicious versions before they reached production; organizations scanning quarterly did not.

 

What it catches that others don’t

Vulnerabilities in the 70–90% of your codebase that your developers did not write. The OWASP Top 10 2025 now ranks Software Supply Chain Failures at #3, and the Verizon 2025 DBIR found third-party breaches at 30% and rising. SCS also catches supply chain-specific attacks — typosquatting, dependency confusion, maintainer account takeover — that do not have CVEs and would not be caught by any other testing method.

 

Limitation

Basic SCA reports every known CVE in every component, regardless of whether the vulnerable function is actually called. This generates noise. The more useful approach is reachability analysis: DerScanner’s hybrid SAST+SCA mode traces the application’s call graph to determine whether a vulnerable method in a dependency is reachable from the application’s code, dramatically reducing false positives.

 

 

SAST vs DAST vs SCA: Comparison Table

 

The SDLC Map Checklist

Code — Run SAST (runs on commit, finds code flaws)

Build — Run  SCA (runs on build, finds dependency vulnerabilities and supply chain threats)

Test/Stage — Run DAST (runs against deployed app, finds runtime and config issues)

Deploy — Generate SBOM per release (compliance evidence for CRA, DORA)

Runtime — Continuous SCA monitoring (new CVEs against deployed components)

 

The three methods are layers that provide security by all means. SAST finds what DAST cannot see (code-level logic). DAST finds what SAST cannot reach (runtime behavior). SCA finds what both miss (third-party risk). 

An AST platform that combines all three — like DerScanner, which delivers SAST across 43+ languages, DAST for running applications, and SCA with SBOM generation, supply chain detection, and reachability analysis in a single platform — eliminates the gaps between methods and provides one consistent evidence trail for auditors, regardless of which regulation they’re checking against.