OWASP Top 10: What Every Developer Must Know

Key Insights

• Injection attacks (SQL, command, LDAP) are prevented by parameterized queries and input validation
• Broken authentication often comes from weak session management, not weak passwords
• Security misconfiguration is the most common vulnerability in production systems

A01: Broken Access Control

Always verify authorization server-side. Never rely on client-side checks:

# Bad: trusting user input
@app.route('/api/users/<user_id>')
def get_user(user_id):
    return db.get_user(user_id)  # Anyone can access any user

# Good: verify ownership
@app.route('/api/users/<user_id>')
@login_required
def get_user(user_id):
    if current_user.id != user_id and not current_user.is_admin:
        abort(403)
    return db.get_user(user_id)

A03: Injection

# Bad: string concatenation
query = f"SELECT * FROM users WHERE name = '{name}'"

# Good: parameterized query
cursor.execute("SELECT * FROM users WHERE name = %s", (name,))

A07: Security Misconfiguration

• Disable directory listing
• Remove default credentials
• Disable unnecessary HTTP methods
• Set security headers (CSP, HSTS, X-Frame-Options)