With APIs projected to become the main attack vector in 2022, companies that downplay the importance of API security risk making the headlines as the next victim of a major data breach—losing customer trust for years to come.
While most API threats are relatively easy to catch using vulnerability scanners, some can remain undetected for years. This makes them a ticking time bomb until bad agents spot them.
Today, we're going to cover one of them. Broken Object Level Authorization (BOLA) vulnerabilities sit at the top of the OWASP API Security Top 10 list. Why is that the case?
Keep reading to find out the answer and learn how to protect yourself from it.
What is Broken Object Level Authorization, and Why Is It #1 on the OWASP Top 10 List?
Object-level authorization is a security measure that controls which users can access which objects, be it database records or files. For example, a user might be allowed to view specific files but not edit or delete them.
Broken object-level authorization (BOLA) vulnerabilities occur when a user is able to access other users' data due to the flaws in authorization controls validating access to data objects.
BOLA vulnerabilities are often caused by insecure coding practices, such as failing to properly validate user input or check permissions before granting access to an object. This happens when an API uses overly permissive access controls or when API resources are not properly protected.
BOLA vulnerabilities lead to devastating data breaches and other ramifications. The USPS hack, one of the largest data breaches in history, happened because of, you guessed it, broken access controls.
“The USPS hack is a classic example of a broken authorization vulnerability. User A was able to authenticate to the API and then pivot and access user B’s and 60 million other people’s information.”
- Dan Barahona, Head of Marketing at Biz Dev at APIsec
How BOLA Actually Works in API Requests
Understanding the BOLA conceptually is one thing; seeing how it plays out at the request level is what makes the risk concrete. In a REST API, a typical authenticated request to fetch an order looks like this:
GET /api/v1/orders/8820
Authorization: Bearer <user_a_token>
The server returns User A's order details. The BOLA vulnerability exists when an attacker simply increments or substitutes the object ID:
GET /api/v1/orders/8821
Authorization: Bearer <user_a_token>
If the server validates that the request is authenticated but doesn't verify that User A owns order 8821, it returns User B's order payment method, shipping address, and all. No privilege escalation required. No stolen credentials. Just a changed number.
The same pattern surfaces in GraphQL through argument manipulation:
graphql
query {
userOrder(orderId: "8821") {
paymentMethod
shippingAddress
personalDetails
}
}
Here are the ways this becomes more dangerous beyond simple ID enumeration:
- Predictable or sequential IDs make enumeration trivial an attacker loops through thousands of object IDs in minutes
- APIs that expose internal database IDs in URLs or response bodies hand attackers their enumeration target directly
- GraphQL APIs that accept object identifiers as arguments are equally exposed, since the attack requires no URL manipulation just a changed argument value
This is why BOLA sits at the top of the OWASP API Security Top 10 the exploit requires no sophisticated tooling, just the ability to read an API response and modify a single value.
Horizontal vs Vertical Privilege Escalation: Where BOLA Fits
Privilege escalation in APIs takes two distinct forms, and understanding the difference clarifies exactly why BOLA is so pervasive and so difficult to catch with standard security tooling.
Vertical privilege escalation means gaining access to functions above your permission level a standard user calling an admin endpoint, or a read-only account executing a write operation. Most security controls are built to catch this. Role checks, permission gates, and access control middleware all target vertical escalation by design.
Horizontal privilege escalation is different. It means accessing another user's data at the same privilege level you're authenticated, your role is valid, but you're reaching into a resource that belongs to someone else. BOLA is horizontal escalation at the API object level, and it's the harder problem to solve because the request looks completely legitimate to every layer of the stack except the one that checks object ownership.
Here are the ways this distinction matters for defense:
- Vertical escalation can often be caught by endpoint-level role checks a standard middleware pattern that most frameworks support natively
- Horizontal escalation requires per-object ownership validation on every resolver and endpoint, which has to be implemented deliberately and tested explicitly
- Standard vulnerability scanners detect missing auth headers and role violations but have no way to know whether the object ID in a request belongs to the authenticated user that context lives in the business logic, not the protocol
This is why BOLA vulnerabilities survive for years in production systems that otherwise pass security audits. The authentication works. The roles are correct. The only thing missing is a single ownership check in the resolver.
How to Protect Your APIs from BOLA Vulnerabilities
Since BOLA vulnerabilities are the most dangerous cluster of API threats, companies need to take proactive steps to prevent them.
Here are the most effective ones.
1. Enforce Robust Authorization Mechanisms
Enforcing robust authorization mechanisms is the first step any organization should take to combat BOLA vulnerabilities.
Many organizations think their APIs are secure because they have strong authentication. But that's not really going to help a whole lot when it comes to BOLA vulnerabilities.
To keep your APIs safe, you need strong authentication mechanisms, but the bigger challenge is ensuring you've got well-controlled authorization policies that you are testing rigorously and continuously to make sure they're free of logic flaws or loopholes.
2. Use Random Universally Unique Identifiers (UUIDs)
The next step is redefining how you approach the process of generating and managing IDs within your API ecosystem. Auto-incrementing IDs absolutely have to go.
As an alternative, use random IDs when creating and accessing APIs. These IDs, commonly referred to as UUIDs, are designed specifically to be difficult for cybercriminals or unauthorized users to guess.
UUIDs are made up of a combination of letters, numbers, and symbols that have no inherent meaning or pattern, making them virtually impossible to guess or reverse-engineer.
Using UUIDs minimizes the risk of malicious tampering, one of the root causes of BOLA vulnerabilities.
3. Laser-focus on Your Business Logic Layer
BOLA vulnerabilities are so tricky because they often lurk in the business logic layer of your APIs.
The implications? It means that BOLA vulnerabilities typically occur due to the flaws in the design of the legitimate functionalities of your APIs rather than bad agents using complex exploits to break into your systems.
That's why it's critical to meticulously test your business logic layer to spot vulnerabilities that are impossible to reliably address upon each release with vulnerability scanners.
“BOLA is already #1 on the OWASP API Security Top 10 list - and for good reasons. API providers do a great job at making sure that users are authenticated to the API, so they want to make sure that legitimate users have access.
But the number one thing that's often overlooked is authorization, ensuring that user A can't access user’s B resources. And it's one thing to hide the resource IDs, but the important factor there is that user A should not be able to access, interact with, or alter user B's resources - at all.”
- Corey Ball, Cybersecurity Consulting Manager and Author of "Hacking APIs"
Multi-Step Workflow Abuse and State-Based BOLA
BOLA doesn't only appear in simple read operations. Some of the most damaging instances occur inside multi-step workflows where object access is validated at step one but not re-validated as the workflow progresses. This is state-based BOLA, and it sits squarely in the business logic layer where automated scanners rarely reach.
A checkout flow illustrates this clearly. Step one authenticates the user and loads their cart ownership is checked, and access is granted. Step two applies a discount code. Step three confirms the order. If the API reuses the session context from step one without re-validating object ownership at step three, an attacker who substitutes another user's order ID at the confirmation step can complete a purchase against someone else's payment method or shipping address.
Here are the ways multi-step BOLA manifests across common API workflows:
- Checkout and payment flows object ownership validated at cart creation but not at payment confirmation, allowing cross-account order manipulation
- Document editing workflows are a collaborative platform that checks document access at open but not at save, allowing an attacker to overwrite another user's content mid-session
- Account update flows profile update endpoints that validate the session at the first step of a multi-part form b,ut process the final PATCH request without re-checking that the target user ID matches the authenticated session
APIsec tests multi-step workflows specifically for state-based BOLA by following complete transaction sequences and validating object ownership at every step not just the entry point. This is where the business logic testing capability matters most, because the vulnerability only becomes visible when you trace the full workflow rather than testing individual endpoints in isolation.
RBAC vs ABAC Validation: When Policy Configuration Creates BOLA
BOLA vulnerabilities don't always come from missing authorization checks; sometimes they come from authorization policies that exist but are misconfigured. Understanding the difference between Role-Based Access Control (RBAC) and Attribute-Based Access Control (ABAC) is important here, because each model has distinct failure modes that lead directly to object-level authorization breaks.
RBAC grants access based on a user's role. A "viewer" role can read, an "editor" role can write, and an "admin" role can delete. The limitation is that RBAC operates at the role level, not the object level. A correctly configured RBAC system confirms that a user with the "viewer" role can read orders but it says nothing about which orders that user is permitted to view. Object ownership validation has to be layered on top, and when it isn't, RBAC becomes a BOLA vulnerability waiting to be found.
ABAC is more granular, granting access based on attributes user ID, department, data classification, time of access. When configured correctly, ABAC can enforce object-level ownership natively. When misconfigured, attribute comparisons that seem correct in isolation produce incorrect results at scale. A tenant ID attribute that isn't propagated consistently across microservices, for example, can grant cross-tenant read access to every user in both tenants.
Here are the ways APIsec validates access control policy enforcement rather than just detecting missing auth:
- Tests whether role boundaries hold at the object level, not just the endpoint level, confirming that a viewer role can't read objects owned by other users even when the endpoint itself is accessible
- Validates ABAC attribute comparisons across different user contexts, flagging cases where attribute-based rules produce incorrect access decisions for specific combinations of user and object attributes
- Detects policy drift between environments authorization rules that are correctly configured in staging but silently relaxed in production due to configuration management gaps
Tenant Isolation Testing for Multi-Tenant SaaS APIs
Multi-tenant SaaS APIs introduce a dimension of BOLA risk that single-tenant systems never face: the possibility that a user in one tenant can access data belonging to a completely separate organization. Cross-tenant BOLA is horizontal privilege escalation at the account boundary level, and the consequences scale with the number of customers sharing the platform.
The attack pattern mirrors standard BOLA exactly substitute a resource ID belonging to a different tenant and observe whether the API enforces tenant isolation or simply validates authentication.
In practice, here are the ways tenant isolation failures surface in SaaS API architectures:
- Shared database architectures without tenant filtering a single database table stores records for all tenants, and the API filters by tenant ID at query time. If that filter is absent from a single endpoint, every record in the table is accessible to any authenticated user regardless of which tenant they belong to
- Tenant ID accepted as a user-supplied parameter APIs that accept tenant context in the request body or query string rather than deriving it from the authenticated session allow attackers to self-assign to any tenant by simply changing the parameter value
- Inconsistent enforcement across microservices tenant isolation enforced in the primary API gateway but not replicated consistently across downstream microservices, creating gaps where direct microservice calls bypass tenant checks entirely
APIsec tests tenant isolation by authenticating as users across different tenant accounts and systematically probing whether object IDs belonging to one tenant are accessible from another. This cross-tenant validation runs across all endpoints — not just the ones where tenant isolation seems obviously necessary — because the riskiest gaps are usually in the endpoints nobody thought to check.
4. Implement the Zero-Trust Security Model
Enforcing the zero-trust security model is another step organizations typically take to protect APIs from BOLA vulnerabilities.
In a traditional security model, authorized and authenticated users are trusted by default.
However, in the zero-trust security model, all users must be authenticated and authorized before accessing any resources. Additionally, the authorized users are constantly monitored to prevent insider threats.
Based on this model, each API call must be authenticated and authorized before it can be executed. Once the user has been authenticated, the authorization mechanisms in place determine whether the user is allowed to access the requested resource.
If the user is not authorized, then the API call will not be executed, making it more difficult for attackers to exploit BOLA vulnerabilities.
5. Ensure Continuous API Security Testing
This is arguably the most effective way to protect APIs from BOLA vulnerabilities. However, here's the rub.
Traditional API security testing tools aren't reliable since vulnerability scanners don't take into account the unique architecture of your API while pen testing is impossible to scale to ensure full coverage with each update.
This is where APIsec comes into play.
APIsec is an industry-leading solution that leverages the power of AI to dissect your API and generate custom-tailored attack scenarios aimed at identifying business logic vulnerabilities.
APIsec is the only reliable way to automatically secure your API from BOLA vulnerabilities and, most importantly, business logic flaws while ensuring full coverage and eliminating human error.
Automated BOLA Detection Across Large API Attack Surfaces
Manual testing for BOLA at any meaningful scale is practically impossible. A modern API with hundreds of endpoints, multiple user roles, and thousands of object types generates a combination space that no pen test engagement can fully cover. An endpoint added in a sprint, a new object type introduced for a feature launch, a role permission adjusted for a customer request any of these can introduce a BOLA vulnerability that won't be found until the next scheduled test, which may be months away.
APIsec approaches this systematically rather than sampling. Here are the ways APIsec automates BOLA detection across large API attack surfaces:
- Role-based cross-testing APIsec authenticates as users across every defined role and attempts to access objects belonging to other roles and other users, validating that ownership checks hold regardless of which role initiates the request
- Object ID substitution at scale, rather than testing a representative sample of endpoints, APIsec substitutes resource identifiers across every endpoint in the API inventory, confirming that object-level authorization is enforced consistently rather than selectively
- Multi-tenant boundary validation cross-account access attempts run across tenant boundaries in SaaS environments, catching isolation failures that only appear when a specific combination of tenant A credentials meets tenant B object IDs
- New endpoint coverage on deployment when new endpoints are added, APIsec automatically generates and runs BOLA test cases for them without requiring manual test authoring, closing the window between deployment and first security test to near zero
This systematic coverage is what makes automated API security testing the only practical defense against BOLA at enterprise scale because the vulnerability doesn't announce itself, and manual testing will always miss the endpoint nobody remembered to include in the scope.
CI/CD Integration for Continuous Authorization Regression Testing
Authorization logic is code. Like any code, it regresses. A refactor that consolidates middleware, a dependency upgrade that changes how tokens are validated, a new endpoint added without the ownership check that every other endpoint has these are the changes that reintroduce BOLA vulnerabilities into APIs that were previously clean. Without authorization regression testing in the CI/CD pipeline, these regressions reach production silently.
Here are the ways integrating BOLA testing into CI/CD prevents authorization regressions from compounding over release cycles:
- Per-deployment authorization baseline APIsec maintains a verified authorization baseline for every endpoint, so any deployment that changes access control behavior for an existing object type is flagged immediately rather than discovered in a future audit
- New object type coverage when a new data model or resource type is introduced, APIsec automatically generates ownership validation tests for it, ensuring that authorization logic for new objects is tested before the endpoint serving them goes live
- Role and permission change detection updates to role definitions or permission scopes trigger a re-run of the full BOLA test suite against affected endpoints, confirming that the intended access change doesn't inadvertently widen object-level access beyond its designed scope
- Deployment gates on authorization failures high-severity BOLA findings block deployment, preventing regressions in authorization logic from reaching production regardless of how the failure was introduced
This makes authorization correctness a continuous, verifiable property of every release rather than something assumed to hold between penetration tests. Given that BOLA is the most exploited vulnerability class in production APIs, building that verification directly into the deployment process is the most direct way to stop it from appearing in your environment.
Sounds too good to be true? Get in touch with our team today to get a free demo.
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