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SAST vs DAST vs IAST: A Tester's Take

SAST, DAST and IAST are the three flavors of automated application security testing that have been on every security roadmap for the last decade. Each finds different bugs and each misses different bugs. Here is an honest comparison, from a view that values manual review most.

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Source code · By Thimmagurudu Bathini · Published · 6 min read · Last reviewed

SAST — Static Application Security Testing

Reads the source code without running it. Strong for: classic injection patterns where the data-flow is short, hardcoded secrets, missing input validation, known dangerous functions. Weak for: business-logic flaws, authentication bugs that depend on flow across multiple requests, anything where the data-flow crosses runtime boundaries (cache, queue, database). High false-positive rate is its biggest cost.

DAST — Dynamic Application Security Testing

Runs the application and sends payloads. Strong for: reflected XSS, classic SQL injection where the response shape changes, configuration issues at the HTTP layer (TLS, headers, cookies). Weak for: authenticated bugs unless the scanner is given good credentials, business logic, anything stored. Lower false-positive than SAST but lower coverage too.

IAST — Interactive Application Security Testing

Instruments the running application and observes data flow during functional testing. Strong for: tracing real data flow through the running app, finding the actual sink for a tainted source. Weak for: requires integration into the build and test environment, can introduce latency, sometimes complicated to deploy at scale.

Where each fits

  • SAST — in CI on every PR, with rules tuned to keep false positives manageable
  • DAST — nightly against staging, plus on-demand against pre-prod
  • IAST — during integration test runs if you have the environment for it
  • Manual review and pen-test — for bugs the tools cannot find, which is most of the high-severity ones

Source code review complements all three.

Written by Thimmagurudu Bathini, BERRY9 IT SERVICES PRIVATE LIMITED, Hyderabad. Questions about your own systems? Request a scoping call or call +91 86868 92922.

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