What is SAST?
Static Application Security Testing (SAST) analyzes source code to find security vulnerabilities before your application runs. Learn how it works and when to use it.
Understanding SAST
SAST (Static Application Security Testing) is a white-box testing method that examines application source code, bytecode, or binary code to identify security vulnerabilities. Unlike dynamic testing, SAST doesn't require the application to be running.
Think of SAST as...
A code reviewer that reads every line of your code looking for security issues. It's like having a security expert review your code 24/7, catching vulnerabilities before they reach production.
How SAST Works
- 1
Code Parsing
The SAST tool parses your source code into an Abstract Syntax Tree (AST) or intermediate representation, understanding the code structure.
- 2
Data Flow Analysis
Traces how data flows through your application, from sources (user input) to sinks (database queries, HTML output) to find tainted data paths.
- 3
Pattern Matching
Compares code against known vulnerability patterns (e.g., SQL injection, XSS) using rules and signatures.
- 4
Report Generation
Produces detailed reports with vulnerability locations, severity ratings, and remediation guidance.
Vulnerabilities SAST Detects
SQL Injection
Unsanitized user input in database queries
Cross-Site Scripting (XSS)
Unescaped user input in HTML output
Hardcoded Secrets
API keys, passwords in source code
Path Traversal
Unvalidated file paths from user input
Command Injection
User input in shell commands
Insecure Deserialization
Deserializing untrusted data
Cryptographic Issues
Weak algorithms, improper key handling
Authentication Flaws
Missing auth checks, weak sessions
SAST: Benefits and Limitations
Benefits
- Early Detection: Finds issues before code runs
- Full Code Coverage: Analyzes all paths, not just executed ones
- Precise Location: Points to exact line of vulnerable code
- CI/CD Integration: Automates security in development pipeline
- No Running App Needed: Works on source code alone
Limitations
- False Positives: May flag safe code as vulnerable
- Can't Find Runtime Issues: Configuration, auth bypass at runtime
- Language Specific: Tools need to support your language
- Scan Time: Large codebases take time to analyze
- Misses Business Logic: Can't understand application context
SAST vs DAST
| Aspect | SAST | DAST |
|---|---|---|
| Testing Type | White-box (source code) | Black-box (running app) |
| When Used | During development | After deployment |
| Requires | Source code access | Running application URL |
| Finds | Code-level vulnerabilities | Runtime vulnerabilities |
| False Positives | More common | Less common |
| Code Location | Exact line number | URL/endpoint only |
Best Practice: Use both SAST and DAST together. SAST catches issues early in development; DAST verifies the deployed application is secure.
Popular SAST Tools
Semgrep
Open Source
Multi-language
CodeQL
Free (GitHub)
Multi-language
SonarQube
Freemium
Multi-language
Snyk Code
Freemium
Multi-language
Checkmarx
Enterprise
Multi-language
Fortify
Enterprise
Multi-language
Frequently Asked Questions
How often should I run SAST scans?
Ideally, on every commit via CI/CD pipeline. At minimum, run scans before each release. More frequent scanning catches issues earlier when they're cheaper to fix.
Do I need SAST if I have code reviews?
Yes. Human reviewers miss things, especially subtle security issues. SAST catches patterns humans overlook and scales to large codebases. Use both together.
How do I reduce false positives?
Configure rules to match your codebase, suppress known false positives, and choose tools with good precision. Some false positives are inevitable—factor in triage time.
Can SAST scan AI-generated code?
Yes. SAST is especially valuable for AI-generated code since AI models can produce vulnerable patterns. Scan all code regardless of origin.
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Last updated: January 2025