SAST vs DAST: what is the difference?
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SAST (Static Application Security Testing) analyzes an application from the inside by examining its source code or binaries without executing it, making it a white-box technique used early in development. DAST (Dynamic Application Security Testing) tests a running application from the outside as a black-box technique, finding runtime and configuration issues. The two are complementary and are often combined with IAST and SCA.
SAST and DAST at a glance
SAST and DAST are two complementary families of application security testing. SAST examines the application from the inside, reading source code, bytecode, or binaries without running the program. DAST examines the application from the outside while it is running, sending inputs and observing responses much as an external user or attacker would.
Neither approach replaces the other. SAST catches issues early and points directly to a line of code, while DAST validates how the application behaves once deployed and configured. Mature programs typically use both.
SAST vs DAST compared
| Dimension | SAST | DAST |
|---|---|---|
| Testing model | White-box, with access to source or binary | Black-box, with no access to source |
| What is analyzed | Source code, bytecode, or compiled binaries | A running, deployed application |
| Code execution | No, the application is not run | Yes, the application must be running |
| Stage in the SDLC | Early, during coding and build | Later, against test or staging environments |
| Strengths | Pinpoints the vulnerable line, finds issues before deployment | Finds runtime, configuration, and environment issues |
| Limitations | More false positives, cannot see runtime behavior | Cannot pinpoint the source line, needs a running app |
| Language awareness | Language and framework specific | Largely language agnostic |
Which one should you use
For most organizations the answer is both, applied at different points in the software development lifecycle. SAST belongs in the developer workflow and build pipeline so issues are caught and fixed cheaply, while DAST belongs against running test or staging environments to confirm behavior under real conditions.
Adding SCA covers the dependencies you did not write, and IAST can tighten accuracy where you can instrument the application. Together these techniques give broader coverage than any single tool.
Keep exploring
- What is vulnerability management?The broader process that application security testing feeds into.
- What is an SBOM?A software bill of materials, closely tied to SCA findings.
- What is a CVE?The identifier SCA tools match dependencies against.
- How to prioritize vulnerabilitiesRanking the findings that testing tools produce.
- CWE directoryThe weakness taxonomy that many SAST findings reference.
- CVSS calculatorScoring the severity of vulnerabilities that testing surfaces.
Frequently asked questions
- What is the main difference between SAST and DAST?
- SAST analyzes the application from the inside by reading code without running it, while DAST tests the application from the outside while it is running. SAST is white-box and DAST is black-box.
- Why does SAST produce more false positives?
- Because SAST reasons about code paths without executing them, it may flag issues that are not actually reachable or exploitable at runtime, which requires triage by a developer or security engineer.
- Can SAST and DAST be used together?
- Yes, and they usually are. SAST runs early in development to catch coding flaws, and DAST runs against a deployed application to catch runtime and configuration issues, giving complementary coverage.
- How do IAST and SCA fit in?
- IAST instruments a running application to combine inside visibility with runtime observation, while SCA analyzes third-party and open-source dependencies for known vulnerabilities. Both complement SAST and DAST.