SAST vs DAST: What's the Difference?
SAST scans source code without running the app; DAST tests a live application by sending real inputs. Both are necessary — they catch different vulnerability classes at different lifecycle stages.
- 1.The Core Distinction
- 2.When SAST is the Right Tool
- 3.When DAST is the Right Tool
- 4.Vulnerabilities Each Catches — and Each Misses
- 5.Using SAST and DAST Together
The Core Distinction
SAST (Static Application Security Testing) and DAST (Dynamic Application Security Testing) are complementary approaches to finding security vulnerabilities in software. The fundamental difference is execution: SAST analyzes code without running it, DAST analyzes behavior by running the application and sending inputs to it.
Every other difference between the two follows from this single distinction.
| Property | SAST | DAST |
|---|---|---|
| Code access required | Yes | No |
| Running app required | No | Yes |
| When it runs | Development, CI/CD | Staging, pre-production |
| What it sees | All code paths | Discoverable endpoints only |
| False positive rate | Higher | Lower (confirmed behavior) |
| False negative rate | Misses runtime behavior | Misses source-level issues |
| Fix guidance | Exact code location and line | Behavioral description |
| Setup complexity | Low | Higher (needs live environment) |
| Speed | Fast to very fast | Slower (sends network requests) |
When SAST is the Right Tool
SAST is best suited for:
- Finding vulnerabilities early in development before code is deployed
- Scanning code changes in CI/CD pipelines before they merge
- Providing developers with exact code locations and line numbers for findings
- Covering code paths that may not be reachable through the application's public interface
- Running without a deployed environment — no staging setup required
When DAST is the Right Tool
DAST is best suited for:
- Confirming that vulnerabilities found in source code are actually exploitable
- Finding runtime and configuration issues invisible to source analysis
- Testing applications where source code is not available (third-party apps)
- Assessing the attack surface of a deployed application from an external perspective
- Regulatory compliance testing that requires demonstrated runtime security
Vulnerabilities Each Catches — and Each Misses
Some vulnerability types are better suited to one approach:
SAST catches, DAST often misses
- Vulnerabilities in code paths that require specific pre-conditions to reach
- Insecure code patterns that may not produce observable errors (time-of-check/time-of-use issues)
- Dead code with security vulnerabilities
- Business logic issues visible in source but not exploitable through external interfaces
DAST catches, SAST often misses
- Server-side misconfigurations not visible in source code
- Race conditions that only appear under concurrent load
- Authentication and session management issues that depend on runtime state
- Vulnerabilities introduced by the deployment environment or infrastructure
Using SAST and DAST Together
The industry consensus is that SAST and DAST are complements, not substitutes. SAST shifts security left — catching vulnerabilities early, when they are cheapest to fix. DAST validates the deployed application — confirming that the security controls actually work at runtime.
A layered approach: SAST in the IDE and CI pipeline during development, DAST against staging before production deployment, and continuous monitoring in both layers.
SAST, DAST, and Autonomous Code Governance
Autonomous code governance uses both: SAST findings drive continuous remediation of source-level vulnerabilities throughout the development cycle, while DAST findings provide runtime validation and identify the subset of vulnerabilities that are confirmed exploitable — the highest-priority remediation targets.
When Hydra receives a DAST-confirmed finding, it treats it as highest-confidence input: the vulnerability is real, it is exploitable, and autonomous remediation should prioritize it accordingly.
Frequently Asked Questions
What is IAST and how does it relate to SAST and DAST?
IAST (Interactive Application Security Testing) instruments the running application to observe its internals during testing. It combines aspects of SAST (source-level visibility) and DAST (runtime observation) by monitoring how the application processes inputs from within. IAST typically has lower false positive rates than either SAST or DAST alone.
Should SAST or DAST block CI/CD pipelines?
SAST is well-suited to blocking CI/CD: it runs fast, provides exact code locations, and integrating it into the PR process catches issues before they merge. DAST typically runs in a later stage against a deployed environment, where blocking on critical findings is appropriate before promotion to production.
Which has more false positives — SAST or DAST?
SAST generally produces more false positives. Because SAST infers behavior from code patterns, it sometimes flags code that appears problematic but is actually safe due to context. DAST confirms findings by observing actual application behavior, so its findings have a lower false positive rate but may miss issues that exist in the code but require specific runtime conditions to trigger.
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