SAST and DAST find different problems, so using both closes blind spots. Static analysis reads source code early and points to the exact line. Dynamic testing attacks the running application and sees configuration, runtime behavior and flaws that only appear when components interact. Together they give earlier detection and fewer misses.
How does each one work?
Static application security testing analyzes source code, bytecode or binaries without running the program. OWASP's overview of source code analysis tools notes strengths such as scanning all code, finding issues early and pointing to the exact location, along with weaknesses: false positives, difficulty with complex runtime behavior, and no view of configuration or deployment.
Dynamic application security testing probes a running application from the outside, the way an attacker would, by sending requests and analyzing responses. It sees what is actually deployed, including servers, headers and authentication flows. It does not need source code, but it only tests what it can reach and usually reports the symptom without the source line.
What does each miss?
SAST misses things that depend on the environment: a missing security header, a permissive cross origin setting, a misconfigured proxy, or an authentication bypass created by how two services are wired together. DAST misses code paths it never triggers, dead branches, and flaws that need specific state to appear. It also gives little help locating the cause.
The two sets of blind spots barely overlap. That is the whole argument for combining them.
Constructed example: one endpoint, two findings
A team ships an export endpoint. SAST flags a query built by string concatenation in the export handler, with file and line, three minutes after the pull request opens. The developer fixes it before merge.
Later, DAST runs against staging and finds that the same endpoint returns a stack trace on malformed input and is reachable without authentication through an old route registered by a separate module. The code scan could not see the second problem, since it came from routing configuration. The dynamic scan could not have named the line for the first problem as quickly.
When should each run?
Run SAST on every pull request, because feedback is cheap while the change is fresh. Run DAST against a deployed test or staging environment, on a schedule or after each deployment, using synthetic data and a scope that excludes destructive actions. NIST's Secure Software Development Framework (SP 800-218) lists code review, analysis and testing among its practices for producing well secured software, and describes using executable testing as well as static methods.
What does it cost to run both?
SAST adds build time and needs rule tuning. DAST needs a stable test environment, test accounts and care around destructive actions. Both need an owner who triages results. The cost is real, but it is smaller than the cost of finding the same flaw in production. Start with the highest risk applications, such as anything internet facing or handling sensitive data, and extend from there.
How do you avoid doubling the noise?
Two tools can mean two long lists. Deduplicate by weakness and location, then rank by exploitability. When both tools flag the same flaw, confidence rises. When only one does, treat it as new information rather than a conflict. Tune rules to your frameworks so false positives do not erode trust, and assign each finding to the owning team.
Safeguard offers static code scanning and dynamic web application scanning in one workflow, plus reachability analysis for dependencies, so findings from code, running apps and libraries appear together and can gate a build.
How to check or apply this
- Run SAST in the pull request and block on high confidence, high impact findings.
- Stand up a staging environment that mirrors production configuration.
- Run authenticated DAST scans there with test accounts for each role.
- Exclude destructive endpoints, or use synthetic data and a reset script.
- Merge results by weakness class and location and rank by exploitability.
- Convert real findings into regression tests.
- Review false positive rates quarterly and tune rules.
Quick check
Can DAST replace SAST?
No. DAST cannot see unexecuted code paths or point to the source line, and SAST cannot see deployed configuration. Each covers gaps in the other.
Which should I run first?
SAST, in the pull request, because early feedback is cheapest. Add DAST once a deployable environment exists.
Sources
- OWASP, Source Code Analysis Tools
- OWASP DevSecOps Guideline
- NIST SP 800-218, Secure Software Development Framework
Last reviewed: 18 October 2026.
