SAST vs DAST vs IAST vs RASP: What Developers Need to Know

Short answer: SAST scans source code without running it, DAST attacks the running application from the outside, IAST watches the running application from the inside with an agent while it is being tested, and RASP is not a testing tool at all: it is an in-app agent that detects and blocks attacks in production. Most teams use SAST early, DAST or IAST before release, and RASP as a runtime safety net.

SAST vs DAST vs IAST vs RASP at a glance

What is SAST (Static Application Security Testing)?

SAST analyzes an application’s source code, bytecode or binaries without executing it, tracing how untrusted data flows through the code to find patterns like SQL injection, cross-site scripting sinks, unsafe deserialization and hard-coded credentials. Because it runs on code, it fits in the IDE, on pull requests and in CI, so developers fix issues before anything ships. The trade-off is noise: SAST cannot see runtime configuration, so it reports some issues that are not exploitable. See our comparison of the best SAST tools.

What is DAST (Dynamic Application Security Testing)?

DAST tests a running application from the outside, the way an attacker would: it crawls the app or API, sends malicious and malformed requests, and judges responses. It needs no access to code and works with any language, which makes it good at catching server misconfiguration, broken authentication and session handling, and injection that is actually reachable. It cannot tell you which line of code is at fault, and it only tests what it can crawl. OWASP ZAP is a widely used open-source DAST scanner.

What is IAST (Interactive Application Security Testing)?

IAST places an instrumentation agent inside the running application (for example in the JVM or .NET runtime) and watches code execution while functional tests, QA testers or a DAST scan exercise the app. Because it sees both the incoming request and the code path it triggers, it reports vulnerabilities with the exact line of code and usually fewer false positives than SAST. Its limits: agents exist only for supported languages and frameworks, and it only finds issues in code that tests actually reach.

IAST vs DAST: the key difference

Both test a running application. DAST sits outside and sees only requests and responses, so it is language-agnostic and easy to point at any URL. IAST sits inside and sees the code, so it can confirm a finding and show where to fix it, but it needs an agent for your stack. Many teams run a DAST scan with an IAST agent installed so they get both views in one test run.

What is RASP (Runtime Application Self-Protection)?

RASP uses the same in-app instrumentation idea as IAST, but in production and for protection rather than testing. It inspects calls such as database queries or file operations at runtime and can block or log an attack, for example an injection payload reaching a query. Think of it as a web application firewall that runs inside the app with full context. RASP buys time, but the underlying bug still needs a code fix. Compare it with perimeter options in our guide to the best WAF tools.

SAST and DAST together: which should you use?

• Start with SAST in pull requests, plus software composition analysis for open-source dependencies.
• Add DAST against staging for every release, especially for internet-facing web apps and APIs.
• Add IAST if you have good automated test coverage on a supported stack and want fewer false positives.
• Consider RASP for high-risk production apps where patching takes time.
• Add fuzzing for parsers and native code. It finds crash-type bugs the other methods miss; see our fuzz testing guide.

To pull all of these findings into one prioritized view, look at ASPM tools. For container images, see tools that eliminate CVEs in container images.

FAQ

Is SAST white-box and DAST black-box? Yes. SAST reads the code (white-box). DAST sees only the running app’s inputs and outputs (black-box). IAST is often called grey-box.

Is RASP the same as IAST? No. They use similar in-app instrumentation, but IAST finds vulnerabilities during testing, while RASP blocks attacks in production.

Can DAST replace SAST? No. DAST misses code paths it cannot reach and cannot point to the faulty line; SAST misses runtime and configuration issues. They cover different gaps.

John King, CISSP, PMP, CISM

John King currently works in the greater Los Angeles area as a ISSO (Information Systems Security Officer). John has a passion for learning and developing his cyber security skills through education, hands on work, and studying for IT certifications.