Broken object-level authorization (BOLA): The silent killer in APIs

Ever handed your car keys to someone and realized they could also access your glovebox, trunk, and even your neighbor’s garage? That’s basically what happens when your API suffers from Broken Object-Level Authorization (BOLA).

APIs are everywhere, driving your mobile apps, web portals, and digital services—but one poorly enforced access control can let attackers run wild. And yet, BOLA remains one of the most overlooked and misunderstood vulnerabilities in the API landscape.

While threats like SQL injection and XSS often make headlines, BOLA quietly lurks in the background, exposing sensitive data and enabling privilege escalation attacks.

Despite being ranked #1 in the OWASP API Security Top 10, it remains widely misunderstood and under-protected.

In this edition of All Things AppSec, we unpack what makes BOLA so deadly, how it operates in the wild, and what you can do to prevent it.

What is BOLA?

Broken object-level authorization (BOLA) occurs when an API improperly enforces permissions for data access. In simple terms, BOLA allows an attacker to manipulate object identifiers in API calls (like user IDs, document IDs, or transaction tokens) to access or modify data they shouldn’t have access to.

Here’s a classic example:

GET /api/users/12345/profile        

If user 12345 is the attacker and they change the request to:

GET /api/users/12346/profile        

—and the API responds with another user’s data, that's BOLA in action.

Why BOLA is so dangerous

• Ease of exploitation: BOLA doesn’t require complex tools or advanced exploits. A simple change to a URL or API parameter can be enough.

• Data exposure at scale: Since APIs handle massive volumes of sensitive data, a single BOLA vulnerability can lead to widespread breaches—think health records, financial information, or private messages.

• Hard to detect: Traditional scanners often miss BOLA because they check for vulnerabilities from a single user’s perspective and don’t simulate privilege misuse.

• Bypasses traditional defenses: Firewalls, WAFs, and even standard authentication are ineffective unless authorization checks are robust and enforced per object.

Real-world BOLA incidents

T-Mobile (2023)

In late 2022, but revealed in January 2023, T-Mobile suffered a breach impacting 37 million customers, stemming from an improperly secured API. Although the company didn’t specify BOLA directly, the nature of the breach—API-based and involving unauthorized data access—mirrored classic BOLA behavior, where attackers were able to retrieve customer data using valid API tokens that were over-privileged or unchecked.

Clubhouse (2021)

The popular audio-chat app exposed user information—including real names, usernames, and social connections—due to a public API with insufficient object-level authorization. While it didn’t lead to immediate damage, it showcased how APIs can silently leak data en masse.

What causes BOLA?

BOLA often stems from flawed assumptions in API design and implementation. Some of the most common causes include:

• Over-reliance on client-side checks: Developers assume users won’t tamper with object IDs or tokens.

• Lack of centralized authorization logic: Inconsistent implementation across endpoints can lead to gaps.

• Improper access control testing: Manual testing or low-coverage automation means BOLA risks remain undetected.

• Speed over security in API deployment: Dev teams often ship APIs quickly to meet business needs, skipping robust access control validation.

Spotting the signs of BOLA

Want to check if your APIs are vulnerable? Here are a few red flags:

• The API accepts object identifiers (like user IDs or document IDs) in the URL or request body without validating them against the logged-in user's permissions.

• The same API endpoint behaves differently depending on what object ID is passed—without returning an “unauthorized” error.

• There’s no internal check to verify ownership or permission before returning a response.

How to prevent BOLA

The good news is BOLA is preventable with the right strategies:

Enforce authorization checks on every object

Authorization should not be a one-time gate. Every time an object (user, resource, document) is accessed or modified, your API should confirm that the requester is allowed to interact with that object.

Avoid relying solely on object IDs from the client

Never trust object references (e.g., /api/user/5678/order/1123) unless they’re validated server-side. Just because the client provides a user ID doesn’t mean that user has permission.

Implement centralized access control

A unified access control layer helps maintain consistency across endpoints and reduces the chance of manual errors.

Use indirect references

Rather than exposing raw object IDs, consider using UUIDs or opaque tokens that are harder to guess or manipulate.

Test for BOLA during API security assessments

Make sure your security testing includes user context-switching scenarios and role-based access misuse to reveal BOLA vulnerabilities.

How Beagle Security helps tackle BOLA

At Beagle Security, we recognize how subtle and devastating BOLA vulnerabilities can be. That’s why our platform includes features that go beyond surface-level scanning:

• Business logic and authorization abuse simulation: We test how your APIs behave under various roles, identity spoofing, and object ID tampering scenarios.

• Shadow API detection: BOLA often hides in undocumented endpoints. Our API discovery feature helps you find and test those forgotten APIs.

• Context-aware testing: Instead of checking access in isolation, we evaluate how different users can interact with objects and resources—exactly how a real attacker would.

• Continuous testing: With each update to your backend or CI/CD pipeline, Beagle ensures your APIs aren’t regressing in security posture.

Conclusion

And that’s BOLA: the quiet assumption that everyone will behave, while attackers freely exploit the lack of object-level checks. It’s subtle, often overlooked, and devastatingly effective. You won't see it coming until someone has already walked out with the goods.

BOLA isn’t some rare edge case. It’s a widespread, persistent problem that’s sitting quietly in many applications. As we continue to build more connected systems, the responsibility to enforce strong, object-level authorization can’t be overstated.

Security isn’t just about gates—it’s about who gets to walk through them and what they’re allowed to touch once they’re inside. With platforms like Beagle Security, you can stop BOLA in its tracks and ensure your APIs don’t become someone else’s attack vector.