Overview
SAST scans an application’s source code at rest to catch insecure patterns before the app ever runs, while DAST attacks a running application from the outside to find exploitable flaws in its live behavior. Teams use both because each catches vulnerability classes the other structurally cannot see.
Comparison Diagram
Comparison Table
| Aspect | SAST | DAST |
|---|---|---|
| What it examines | Source code, bytecode, or binaries at rest | A running, deployed application from outside |
| Access level | White-box — full visibility into code internals | Black-box — only sees inputs and outputs like an attacker |
| When in SDLC | Early, during coding and in CI on every commit | Later, once a build is deployed to a test or staging environment |
| Environment needed | None — analyzes files directly, no app needs to run | A live, reachable instance of the application |
| Vulnerability classes found | Insecure code patterns: SQL string building, hardcoded secrets, unsafe deserialization | Exploitable runtime behavior: auth bypass, injection responses, misconfigured headers |
| Language/stack dependency | Tied to the language and framework being parsed | Language-agnostic — probes over HTTP/HTTPS regardless of stack |
| False positive tendency | Higher — flags patterns that may not be reachable or exploitable | Lower — findings are confirmed by actual exploit attempts |
| Remediation output | Exact file and line number to fix | Vulnerable URL, parameter, and request/response evidence |
Key Differences
- SAST inspects source code without running it; DAST attacks a live instance without seeing its internals
- SAST fits early into CI pipelines per-commit; DAST needs a deployed build to test against
- SAST pinpoints the exact line number; DAST reports the vulnerable endpoint and payload
- SAST is prone to false positives from unreachable code paths; DAST confirms via actual exploitation
- SAST misses runtime configuration flaws that DAST catches, like missing security headers or session issues
When to Use Each
SAST
- Shift-left in CI: SAST runs on every pull request without needing a deployed environment, catching insecure code before merge.
- Pinpointing exact fix location: Developers get the specific file and line to patch, shortening remediation time.
- Auditing proprietary logic: Only SAST can see business logic and internal functions never exposed over the network.
DAST
- Pre-release penetration testing: DAST validates the deployed application the way a real attacker would interact with it.
- Testing third-party or legacy components: DAST works without source access, useful for vendored code or compiled binaries.
- Catching runtime misconfigurations: Issues like exposed debug endpoints or weak TLS settings only appear once the app is actually running.