Security Code Analysis — What It Is and How to Do It

What is security code analysis?

Security code analysis (also called Static Application Security Testing or SAST) examines source code without executing it to find security vulnerabilities. It differs from penetration testing, which attacks a running application. SAST finds issues earlier in development — before code ships to production.

According to IBM's Cost of a Data Breach report, vulnerabilities found in development cost ~$80 to fix. The same vulnerability found in production costs ~$7,600. Security code analysis is the most cost-effective security investment available.

The OWASP Top 10 lists the most critical web application security risks. Security code analysis should check for all of them.

Standard linters check style. Security analysis understands data flow — where untrusted input goes.

❌ Linter passes — security tool flags

# ESLint/Pylint: no issues found
@app.route('/user/<int:user_id>')
def get_user(user_id):
    doc_path = request.args.get('doc')
    return send_file(f"/docs/{doc_path}")  # Path traversal!
    # Linter: valid syntax, no style issues
    # Security: user controls doc_path → ../../etc/passwd

✅ After security analysis fix

@app.route('/user/<int:user_id>')
def get_user(user_id):
    doc_path = request.args.get('doc', '')
    safe_path = os.path.realpath(os.path.join('/docs', doc_path))
    if not safe_path.startswith('/docs/'):
        abort(403)
    return send_file(safe_path)

Four practical approaches, from free and instant to comprehensive paid tools.