SAST vs DAST vs IAST: Choosing the Right Mix for Your Pipeline

Cybersecurity

Static, dynamic, and interactive application security testing each find different bugs and miss different bugs. The right mix depends on the language, the deployment model, and the engineering culture. We unpack what each tool actually does well, where the marketing claims fall apart, and which combinations are worth the build minutes.

By Arjun Raghavan, Security & Systems Lead, BIPI · August 17, 2023 · 10 min read

Most security tooling pitches sound interchangeable. Find vulnerabilities in your code, integrate with your CI, reduce risk. The reality is that SAST, DAST, and IAST find different bugs, miss different bugs, and produce different shapes of false positives. Picking the wrong one for the language or the deployment model wastes build minutes and burns out the AppSec team.

SAST: source analysis without execution

Static application security testing reads the source code, builds a model of data flow and control flow, and looks for patterns that match known vulnerability classes. It is good at finding injection sinks, hardcoded secrets, weak crypto, and unsafe deserialization. It is bad at finding logic bugs, authorization flaws, and anything that depends on runtime state.

• Strong on injection, crypto misuse, unsafe APIs, hardcoded secrets
• Weak on auth logic, race conditions, business logic flaws
• False positive rate is the dominant cost, expect 60 to 80 percent on first run

SemGrep, CodeQL, and the commercial Checkmarx and Veracode tools all live in this category. SemGrep is the easiest to tune and the cheapest to operate at scale. CodeQL has the deepest analysis when you can afford the build time.

DAST: black-box runtime probing

Dynamic application security testing runs against a deployed instance and probes it with malicious inputs. It is good at finding what an external attacker would find. SSRF, XSS, authentication bypasses, missing security headers, and exposed admin endpoints all surface here. It is bad at finding anything that requires knowing the codebase.

OWASP ZAP and Burp Suite are the standards. Both can be scripted into CI against a staged deployment. The catch is that DAST requires a working test environment with realistic data, which is itself a meaningful platform investment.

IAST: runtime instrumentation

Interactive application security testing instruments the running application and observes data flow at runtime. It combines the precision of SAST about which line of code is involved with the realism of DAST about which paths actually execute. Contrast Security and Synopsys Seeker are the main commercial offerings.

IAST shines for high-coverage QA environments where the test suite already exercises most of the application. It struggles in low-coverage environments where the instrumentation has nothing to observe.

An IAST license without a test suite is an expensive way to confirm what your unit tests already missed.

What we recommend by language

1. JavaScript and TypeScript: SemGrep plus npm audit plus a ZAP scan against staging
2. Python: SemGrep plus pip-audit plus Bandit for the legacy patterns
3. Java and Kotlin: CodeQL for depth, Trivy for dependencies, ZAP for runtime
4. Go: SemGrep plus govulncheck plus ZAP
5. C and C++: a real compiler-based SAST like Coverity or CodeQL, no shortcuts here

The integration that actually works

Run SAST on every PR, scoped to the diff, with a tight ruleset that has been tuned to your codebase. Run DAST nightly against a staging deployment with a known baseline of accepted findings. Reserve IAST for the pre-production environment where you have meaningful QA traffic. Aggregate all findings into a single tracker so the AppSec team is not chasing duplicates across three tools.

The triage problem

All three tools produce false positives. The teams that succeed invest in triage automation. Tag findings with reachability data from runtime, suppress patterns that have been reviewed and waived, and feed the result into the same ticketing system the engineers already use. The teams that fail dump raw findings into a security dashboard nobody reads.

Closing

AppSec tooling is a portfolio decision, not a checkbox. The right mix depends on your stack, your test maturity, and your team capacity. Buying three tools because they were on the Magic Quadrant is a common failure pattern. Pick one, tune it, integrate it, and only add the next one when you have run the first one for a quarter.

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