SAST vs DAST • DeepSource

Overview

SAST and DAST represent two fundamental approaches to application security testing. Each serves a distinct purpose in a comprehensive security testing strategy, and understanding their differences is crucial for effective implementation.

SAST (Static Application Security Testing)

How it Works

Analyzes source code, bytecode, or binary code without executing the application
Scans from the "inside out" by examining the code structure
Integrated early in the development cycle (shift-left security)

Strengths

Early detection of vulnerabilities
Complete code coverage
Language and framework-specific checks
Identifies issues before deployment

Limitations

Can produce false positives
Cannot detect runtime issues
Limited to known patterns and rules

Example Vulnerabilities Detected

# SAST would flag these security issues:

# 1. SQL Injection vulnerability
def get_user(user_id):
    query = f"SELECT * FROM users WHERE id = {user_id}"  # Vulnerable
    return db.execute(query)

# 2. Hardcoded credentials
API_KEY = "1234-abcd-5678-efgh"  # Vulnerable

# 3. Insecure cryptographic function
def hash_password(password):
    return md5(password).hexdigest()  # Vulnerable

DAST (Dynamic Application Security Testing)

How it Works

Tests running applications in production-like environments
Simulates external attacks on the application
Scans from the "outside in" by examining application behavior

Strengths

Finds runtime vulnerabilities
Minimal false positives
Language/framework agnostic
Identifies configuration issues

Limitations

Cannot pinpoint exact code locations
Limited to exposed interfaces
Requires a running application
May miss some vulnerability types

Example Vulnerabilities Detected

# DAST would identify these runtime issues:

# 1. Insecure API endpoint
@app.route('/api/user-data')
def get_user_data():
    # DAST would detect:
    # - Missing authentication
    # - Sensitive data exposure
    return jsonify(user.personal_info)

# 2. Misconfigured headers
@app.after_request
def add_headers(response):
    # DAST would detect missing security headers
    return response

Best Practices

Use both SAST and DAST for comprehensive coverage
Implement SAST early in development
Run DAST in staging/pre-production

Conclusion

While SAST and DAST have different approaches and capabilities, they complement each other effectively. A mature application security program should incorporate both methods to maximize vulnerability detection and minimize security risks throughout the development lifecycle.