SAST vs DAST
Static vs Dynamic Application Security Testing: understand the differences, know when to use each, and learn how to combine them for comprehensive security coverage.
Quick Comparison
SAST
Analyzes source code without running the application
DAST
Tests the running application from the outside
Detailed Comparison
| Aspect | SAST | DAST |
|---|---|---|
| Testing Type | White-box (inside-out) | Black-box (outside-in) |
| Input Required | Source code | Running application URL |
| When in SDLC | Development (early) | Testing/Production (late) |
| Coverage | All code paths | Only discoverable endpoints |
| False Positives | Higher | Lower |
| Remediation Info | Exact line number | URL/endpoint only |
| Language Support | Must support language | Any technology |
| Runtime Issues | Can't detect | Detects |
| Business Logic | Can't understand | Limited understanding |
| Scan Speed | Fast (minutes) | Slower (hours) |
What Each Approach Finds Best
SAST Excels At
- Hardcoded secrets and credentials
- SQL injection patterns in code
- Buffer overflows and memory issues
- Insecure cryptographic implementations
- Code quality and maintainability issues
- Vulnerable dependency versions
DAST Excels At
- Authentication and session issues
- Server misconfigurations
- Missing security headers
- SSL/TLS vulnerabilities
- CORS and CSRF issues in practice
- Runtime injection exploitability
When to Use Each
Use SAST When...
- • On every commit via CI/CD pipeline
- • During code review before merge
- • When you need to find the exact vulnerable code line
- • Checking for hardcoded secrets before commit
- • Auditing code quality and security patterns
Use DAST When...
- • After deploying to staging/production
- • Validating security configurations
- • Testing third-party integrations
- • Verifying SAST findings are exploitable
- • Compliance testing (PCI DSS, etc.)
Use Both Together...
- • For comprehensive security coverage
- • When security is critical (fintech, healthcare)
- • In mature DevSecOps pipelines
- • Before major releases
The Best Approach: Use Both
SAST and DAST are complementary, not competing approaches. Together they provide defense in depth:
Coverage improves dramatically: Studies show SAST finds 40-60% of vulnerabilities, DAST finds 30-50%, but together they can catch 80-90% of common vulnerabilities.
Frequently Asked Questions
If I can only choose one, which should I pick?
For early-stage startups: start with SAST in CI/CD—it's cheaper to fix issues in code than production. Add DAST once you have a live application. If you're already in production with security concerns, start with DAST to find exploitable issues immediately.
Do SAST and DAST replace penetration testing?
No. Automated tools find common vulnerability patterns. Pentesting adds human creativity to find business logic issues, complex attack chains, and novel vulnerabilities that automated tools miss. Use all three for best coverage.
How do I handle the false positives from SAST?
1) Configure rules to match your codebase, 2) Suppress known false positives, 3) Use DAST to verify if SAST findings are exploitable, 4) Prioritize findings in security-critical code paths first.
What about IAST (Interactive AST)?
IAST combines SAST and DAST by instrumenting the running application. It provides code-level detail with runtime confirmation. Consider IAST if you need the best of both worlds and can support the instrumentation overhead.
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Last updated: January 2025