Introduction

Broken Access Control is a critical security vulnerability that occurs when an application does not properly enforce access controls, allowing unauthorized users to access restricted resources or perform actions they should not be able to. This can lead to data breaches, unauthorized data manipulation, and other serious security issues.

Key Concepts

Access Control: Mechanisms that restrict access to resources based on user roles, permissions, and policies.
Broken Access Control: Failures in enforcing these mechanisms, leading to unauthorized access.
Common Scenarios:
- Vertical Privilege Escalation: Lower-privileged users gain higher-level privileges.
- Horizontal Privilege Escalation: Users access resources or functions of other users with the same privilege level.

Examples of Broken Access Control

Example 1: Insecure Direct Object References (IDOR)

An application allows users to access resources by specifying a unique identifier in the URL. If the application does not verify the user's authorization to access the resource, it can lead to IDOR.

# Example of insecure direct object reference
@app.route('/user/<user_id>')
def get_user_profile(user_id):
    user = User.query.get(user_id)
    return render_template('profile.html', user=user)

Explanation: In this example, any user can access any other user's profile by changing the user_id in the URL.

Example 2: Missing Function Level Access Control

An application does not enforce access control checks on sensitive functions, allowing unauthorized users to perform restricted actions.

# Example of missing function level access control
@app.route('/admin/delete_user/<user_id>', methods=['POST'])
def delete_user(user_id):
    user = User.query.get(user_id)
    db.session.delete(user)
    db.session.commit()
    return redirect(url_for('admin_dashboard'))

Explanation: In this example, any user can delete any other user by accessing the URL, as there is no check to ensure the user has admin privileges.

Preventing Broken Access Control

Implement Role-Based Access Control (RBAC): Define roles and permissions clearly and enforce them throughout the application.
Use Secure Frameworks: Leverage security features provided by frameworks to manage access control.
Validate User Permissions: Always check user permissions before granting access to resources or functions.
Least Privilege Principle: Grant users the minimum level of access necessary for their role.
Regular Audits and Testing: Conduct regular security audits and penetration testing to identify and fix access control issues.

Practical Exercise

Exercise: Implementing Access Control

Objective: Secure the delete_user function to ensure only admin users can delete other users.

Instructions:

Define an is_admin attribute for the User model.
Modify the delete_user function to check if the current user is an admin before allowing the deletion.

Solution:

# Step 1: Define an is_admin attribute for the User model
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    is_admin = db.Column(db.Boolean, default=False)

# Step 2: Modify the delete_user function to check for admin privileges
@app.route('/admin/delete_user/<user_id>', methods=['POST'])
@login_required
def delete_user(user_id):
    if not current_user.is_admin:
        abort(403)  # Forbidden
    user = User.query.get(user_id)
    if user:
        db.session.delete(user)
        db.session.commit()
    return redirect(url_for('admin_dashboard'))

Explanation:

The is_admin attribute is added to the User model to indicate whether a user has admin privileges.
The delete_user function now checks if the current user is an admin before proceeding with the deletion. If the user is not an admin, a 403 Forbidden error is returned.

Common Mistakes and Tips

Assuming Client-Side Checks Are Sufficient: Always enforce access control on the server side. Client-side checks can be bypassed.
Hardcoding Access Control Logic: Use centralized access control mechanisms to avoid inconsistencies and errors.
Ignoring Indirect Access Paths: Ensure all paths to sensitive resources are protected, including indirect access through APIs or background processes.

Conclusion

Broken Access Control is a serious vulnerability that can lead to unauthorized access and data breaches. By understanding common scenarios and implementing robust access control mechanisms, you can significantly enhance the security of your web applications. Regular audits and adherence to best practices are essential to maintaining secure access controls.

A5: Broken Access Control

Introduction

Key Concepts

Examples of Broken Access Control

Example 1: Insecure Direct Object References (IDOR)

Example 2: Missing Function Level Access Control

Preventing Broken Access Control

Practical Exercise

Exercise: Implementing Access Control

Common Mistakes and Tips

Conclusion

OWASP Course: Guidelines and Standards for Web Application Security

Module 1: Introduction to OWASP

Module 2: Main OWASP Projects

Module 3: OWASP Top Ten

Module 4: OWASP ASVS (Application Security Verification Standard)

Module 5: OWASP SAMM (Software Assurance Maturity Model)

Module 6: OWASP ZAP (Zed Attack Proxy)

Module 7: Best Practices and Recommendations

Module 8: Practical Exercises and Case Studies

Module 9: Evaluation and Certification