How to Identify and Fix BOLA Vulnerabilities in Your APIs (2025)

By Clinton Nwezeaku
on April 8, 2025

Broken Object Level Authorization (BOLA), also known as Insecure Direct Object References (IDOR), is one of the most critical vulnerabilities affecting APIs. It occurs when an application fails to properly enforce authorization on object-level access, allowing attackers to manipulate object identifiers to gain unauthorized access to data. As APIs continue to power the backbone of modern applications, securing them against BOLA vulnerabilities is imperative for developers and security professionals.

In this technical guide, we will dive deep into how to identify, test, and remediate BOLA vulnerabilities in APIs.

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Understanding BOLA

-Learn More About Broken Object Level Authorization

At its core, BOLA is a failure to restrict access to objects based on a user’s authorization. Consider a URL like:

				
					https://api.example.com/users/12345

If an authenticated user can modify the ID (e.g., to /12346/) and access another user’s profile without restriction, the API is vulnerable to BOLA.

Why Is BOLA Dangerous?

It allows attackers to read, modify, or delete data they do not own.
Often difficult to detect with automated tools.
Common in RESTful and GraphQL APIs.

Step 1: Identifying BOLA Vulnerabilities

1.1 Understand the Application Context

Begin with mapping out all API endpoints and understanding how object references are used. Focus on resources such as:

User profiles
Order details
Messages
Documents

1.2 Manual Testing with API Clients

Use tools like Postman, Insomnia, or Burp Suite to manipulate API requests:

Log in as a normal user
Interact with an API endpoint to get a valid object ID (e.g., user ID, document ID)
Modify the ID in subsequent requests to test access to unauthorized data

Example Test:

				
					Original request:
GET /api/messages/789

Modified request:
GET /api/messages/790

If the server responds with the content of message 790 without proper access control, it is a BOLA vulnerability.

1.3 Test with Multiple User Roles

Make sure to test requests across:

Regular users
Admins
Guest accounts

Access control often varies by role and can expose hidden BOLA issues.

1.4 Analyze API Documentation

Review OpenAPI/Swagger specifications. APIs with predictable and sequential object IDs are more prone to BOLA.

Step 2: Fixing BOLA Vulnerabilities

2.1 Implement Object-Level Authorization Checks

Ensure that every request for an object includes a check to confirm that the user is authorized to access it.

Example in Python (Flask):

				
					@app.route('/api/orders/<order_id>')
def get_order(order_id):
    order = Order.query.get(order_id)
    if order.user_id != current_user.id:
        return {"error": "Unauthorized"}, 403
    return order.serialize()

2.2 Avoid Relying Solely on Frontend Restrictions

Do not depend on client-side logic to enforce authorization. Always perform checks on the server side.

2.3 Use Indirect References

Instead of exposing sequential or guessable IDs (e.g., /user/1001), use UUIDs or opaque tokens.

Before:

				
					GET /api/documents/45

After:

				
					GET /api/documents/ae7f4d89-3221-4c65-91a2-d7f6e1c2f478

2.4 Adopt Role-Based Access Control (RBAC) or Attribute-Based Access Control (ABAC)

Implement RBAC/ABAC systems to determine access permissions based on user roles or attributes.

2.5 Centralize Authorization Logic

Centralizing object-level access control logic reduces the risk of inconsistent checks across multiple endpoints.

Step 3: Automating BOLA Detection and Prevention

3.1 Use Static Application Security Testing (SAST) Tools

SAST tools can detect insecure coding patterns that lead to BOLA vulnerabilities.

3.2 Employ Dynamic Application Security Testing (DAST) and API Scanners

Tools like:

OWASP ZAP
Burp Suite Pro
Postman Security
StackHawk

These tools can simulate attacks by tampering with object IDs in real API calls.

3.3 Integrate Authorization Tests in CI/CD Pipelines

Write automated tests that verify authorization checks are in place for critical endpoints during each deployment.

Best Practices to Prevent BOLA

Design with Least Privilege in Mind: Grant users the minimum access required.
Audit and Log Access Attempts: Monitor logs for unauthorized access attempts or object ID enumeration.
Regularly Update API Documentation: Ensure all endpoints are accurately documented to assist with security reviews.
Conduct Regular Code Reviews: Focus on authorization logic and ensure object-level access control is enforced.
Educate Developers: Train your dev team to recognize and defend against BOLA vulnerabilities.

Conclusion

BOLA vulnerabilities remain a top concern in API security, particularly due to their simplicity and severity. Identifying and fixing BOLA requires a combination of manual testing, secure coding practices, and automated security tools. By implementing robust authorization checks, using indirect object references, and embracing secure development lifecycles, development teams can significantly reduce the risk of BOLA in their APIs.

Security is not a one-time task. Make BOLA prevention a continuous part of your API development and testing process. By doing so, you’ll not only protect sensitive data but also build trust with your users and partners in an increasingly connected digital landscape.

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