What is SAST (Static Application Security Testing)?

Static Application Security Testing (SAST) is a white-box security testing approach that examines application source code, bytecode, or compiled binaries to identify security vulnerabilities. SAST tools analyze code structure and data flow to find issues like SQL injection, cross-site scripting (XSS), buffer overflows, and insecure cryptographic practices before the application runs.

How SAST works

SAST tools typically perform several types of analysis:

1. Semantic analysis: Parsing code into an abstract syntax tree (AST) to understand structure and identify dangerous patterns
2. Data flow analysis: Tracking how data moves through the application to find paths from untrusted input to sensitive operations
3. Control flow analysis: Understanding execution paths to identify unreachable code and logic vulnerabilities
4. Taint analysis: Following potentially malicious input through the codebase to detect injection vulnerabilities

Advantages of SAST

Early detection: SAST can run on code before it's deployed or even compiled. This makes it possible to catch vulnerabilities during development when they're cheapest to fix.

Complete coverage: Unlike DAST, which only tests exposed endpoints, SAST examines all code paths including error handlers and rarely-executed branches.

Precise location: SAST identifies exactly where vulnerabilities exist in code, often down to the specific line number.

Scalability: Once configured, SAST tools can analyze large codebases automatically without requiring a running application or test environment.

Limitations

False positives: SAST tools often flag code that looks suspicious but isn't actually vulnerable in context. High false positive rates can cause developers to ignore results.

No runtime context: SAST cannot detect issues that only manifest at runtime, such as configuration errors or environment-specific vulnerabilities.

Language coverage: Each programming language requires specific analyzer support. Polyglot applications need multiple tools.

SAST in the development lifecycle

Modern SAST implementations integrate with CI/CD pipelines and version control systems, running automatically on every pull request. This shift-left approach catches vulnerabilities before they reach production.

SAST is most effective when combined with DAST for runtime testing and SCA for dependency analysis, forming a comprehensive application security program.

See also: DAST, Static Analysis, Shift-Left Security, Taint Analysis