Access Control

Access Control

Definition:

Access control, in the context of web applications, ensures that users can only perform actions and access data/resources they're authorized to. It restricts what operations authenticated users can perform, ensuring they can't access or modify data beyond their permissions.

Key Points:

• A lack of proper access control can lead to unauthorized data access, modification, or even full system compromise.

• There are various models of access control: Discretionary Access Control (DAC), Mandatory Access Control (MAC), Role-Based Access Control (RBAC), and Attribute-Based Access Control (ABAC) being some common ones.

Types:

1. Vertical Access Control:

   • Differentiates between user roles. E.g., User vs. Admin.

2. Horizontal Access Control:

   • Restricts access to certain data within a role. E.g., A user can only view their own profile.

Example Scenarios:

1. Vertical Access Control: A simple RBAC system where users and admins have different permissions.

   python

• # Python example with Flask
  from flask import Flask, request, redirect
  
  app = Flask(__name__)
  
  # Mock database
  USERS = {"alice": {"role": "user"}, "bob": {"role": "admin"}}
  
  @app.route('/admin_panel')
  def admin_panel():
      username = request.args.get('username')
      user = USERS.get(username)
      if user and user['role'] == 'admin':
          return "Welcome to the admin panel!"
      else:
          return redirect('/unauthorized')
  
  @app.route('/unauthorized')
  def unauthorized():
      return "You're not authorized to access this resource."

• Horizontal Access Control: Users can only modify their own profile information.

  python

1. # Python example with Flask
   from flask import Flask, request, jsonify
   
   app = Flask(__name__)
   
   # Mock database
   USERS = {
       "alice": {"password": "alice123", "profile": {"email": "[email protected]"}},
       "bob": {"password": "bob123", "profile": {"email": "[email protected]"}}
   }
   
   @app.route('/view_profile')
   def view_profile():
       username = request.args.get('username')
       auth_user = get_authenticated_user()  # A function to get the currently authenticated user
       if username == auth_user:
           return jsonify(USERS[username]['profile'])
       else:
           return jsonify({"error": "Access denied"})
   

Mitigation:

1. Default Deny:

   • Always start with a default-deny posture. Only grant access if explicitly allowed.

2. Principle of Least Privilege (PoLP):

   • Users should only have the minimum permissions necessary to do their tasks.

3. Regular Audits:

   • Continuously review and audit permissions to ensure they are appropriate.

4. Centralized Access Control Management:

   • Manage permissions centrally to reduce errors and inconsistencies.

5. Use Established Libraries/Frameworks:

   • Many web frameworks offer built-in tools for access control (e.g., Django's permissions system, Spring Security for Java).

6. Consistent Error Messages:

   • Do not differentiate between "resource not found" and "access denied" as it can leak information about which resources exist.

Bypass Techniques:

1. IDOR (Insecure Direct Object References):

   • When resources (like files or database entries) can be accessed directly by modifying values in the URL or request (like changing the ID).

2. Role Impersonation:

   • If the application relies on client-side data (like cookies or hidden form fields) to determine a user's role, an attacker might modify this data to impersonate another role.

3. Forced Browsing:

   • Attackers try to navigate directly to restricted pages by manually entering the URL.

4. Verb Tampering:

   • Some applications might restrict operations based on HTTP verbs (like GET or POST). Attackers might change the verb to bypass restrictions.

Conclusion:

Access control is fundamental in web application security. Without it, unauthorized users can access or modify sensitive data, leading to breaches and system compromise. Implementing strong and consistent access control policies, regularly auditing permissions, and staying aware of common bypass techniques are crucial for maintaining a robust defense against unauthorized access attacks.