BOLA vs BFLA: Key differences for API security teams

BOLA vs BFLA is one of the most common points of confusion in API security. Both are authorization failures, both are widespread, and both appear in the OWASP API Security Top 10 – yet they occur at different layers and require different fixes.

Broken object-level authorization (BOLA) has held the #1 position in the OWASP API Security Top 10 since the list was first introduced in 2019, while broken function-level authorization (BFLA) continues to appear as a top-tier risk in real-world breach data. Both are critical since most API attacks rely on bypassing authorization, not authentication. Research shows that the vast majority of attacks originate from authenticated sessions, with attackers using valid credentials and exploiting authorization gaps rather than breaking login mechanisms.

The confusion has real consequences. Teams routinely misclassify findings, design tests that only cover one failure mode, or implement controls that solve the wrong problem. A developer who fixes a BOLA vulnerability by adding object-level ownership checks has not addressed a BFLA vulnerability in the same endpoint. A security team that tests only with a single user misses both entirely.

Understanding the difference between BOLA and BFLA is foundational to building an effective API security program. This guide breaks down BOLA vs BFLA in practical terms, including how they differ, how they combine, and how to test for both. 

BOLA and BFLA definitions

BOLA (Broken Object Level Authorization) – OWASP API1:2023 – occurs when an API authenticates a user and permits them to access an endpoint, but fails to verify that the specific object being requested belongs to that user. The function is authorized; the object is not. BOLA is horizontal privilege escalation: a user accessing another user's data at the same privilege level.

BFLA (Broken Function Level Authorization) – OWASP API5:2023 – occurs when an API fails to verify that an authenticated user has permission to invoke a specific function or endpoint at all. The user is authenticated; the function is not permitted for their role. BFLA is typically vertical privilege escalation: a lower-privilege user invoking a higher-privilege function.

The core distinction: Object vs. function authorization

Authorization in modern APIs is a layered decision process, and BOLA and BFLA represent failures at different points in that process.

Layer 1: Function-level authorization (BFLA layer)

At this layer, the API decides whether a user is allowed to invoke a function at all. This is typically implemented through role-based or attribute-based access control – mapping roles or permissions to endpoints and HTTP methods. If a user can execute a function their role should not permit, the failure is BFLA.

Layer 2: Object-level authorization (BOLA layer)

If the function-level check passes, the API must determine whether the user is authorized for the specific object referenced in the request. This is enforced by scoping data access to the current user or tenant. If the API returns another user’s data, the failure is BOLA.

The following flow illustrates where each vulnerability occurs in the request lifecycle:

OWASP makes this boundary explicit. In BOLA, the user is expected to access the endpoint – the violation happens at the object level by design. If a user can reach a function they should not be able to call at all, that is BFLA.

In practice, this means BFLA is a role enforcement problem, while BOLA is a data ownership enforcement problem. Fixing one layer does not automatically address the other.

BOLA vs BFLA: Side-by-side attack pattern comparison

BOLA in action: The object ID manipulation pattern

Scenario: An API exposes order data by ID:

GET /api/orders/1001
Authorization: Bearer USER_A_TOKEN

An attacker requests a different ID:

GET /api/orders/1002
Authorization: Bearer USER_A_TOKEN

The only change between these two requests is the object identifier. The user remains the same, but the API returns data for a different user.

This is BOLA. The user is authorized to call the endpoint itself, but the API fails to verify ownership of the object. A secure API should return a 403 or equivalent error when the object does not belong to the authenticated user.

BOLA vulnerabilities are typically discovered and exploited by manipulating identifiers – incrementing numeric IDs, swapping UUIDs, or replaying requests across user sessions. The same methods are used by pentesters and scanners to detect BOLA in APIs.

This pattern has appeared in real-world incidents. In the 2024 Spoutible breach, authenticated API requests exposed other users’ sensitive data because object-level authorization checks were missing.

BFLA in action: The function invocation pattern

Scenario: An administrative endpoint allows a regular user to send a request to delete a record by ID:

DELETE /api/admin/users/456
Authorization: Bearer STANDARD_USER_TOKEN

The request is valid at the protocol level, but it targets a function that should be restricted to higher-privilege roles.

This is BFLA. The user should not be able to invoke the function at all. A secure implementation would block this request before execution based on the user’s role.

BFLA vulnerabilities are typically discovered by enumerating endpoints and testing access from lower-privilege accounts – especially admin paths, internal APIs, and undocumented HTTP methods.

HTTP method BFLA: The hidden exposure pattern

GET /api/documents/doc-123
Authorization: Bearer USER_TOKEN
→ 200 OK

DELETE /api/documents/doc-123
Authorization: Bearer USER_TOKEN
→ 200 OK

The same resource is protected for read access but exposed for deletion.

The API enforces authorization for read operations but fails to apply the same controls to destructive methods. Authorization must be enforced consistently across all HTTP methods, not just GET. Method-level inconsistencies like this are a common source of BFLA.

Role self-modification BFLA: The privilege escalation pattern

PUT /api/users/me
Authorization: Bearer USER_TOKEN

{"role":"admin"}

This allows a standard user to directly modify a security-sensitive field that should never be user-controlled.

The critical impact is not the response itself, but that subsequent requests now execute with elevated privileges, confirming the role change has been applied.

When BOLA and BFLA combine: The chained attack

In real applications, BOLA and BFLA often reinforce each other rather than appearing in isolation.

Chain pattern 1: BOLA enables BFLA

In this scenario, BOLA exposes sensitive information, and BFLA uses it to escalate privileges.

In step 1, BOLA exposes sensitive identifiers:

GET /api/users/1050
Authorization: Bearer USER_TOKEN
{"userId":1050,"role":"admin"}

In step 2, BFLA uses that information:

POST /api/admin/impersonate
Authorization: Bearer USER_TOKEN
{"targetUserId":1050}

Chain pattern 2: BFLA enables BOLA at scale

Here, BFLA provides bulk access, and BOLA turns it into large-scale data extraction.

In step 1, BFLA exposes bulk data:

GET /api/admin/users
Authorization: Bearer USER_TOKEN

In step 2, BOLA exploits it. An attacker can iterate through all user IDs and extract data from endpoints that lack object-level validation.

Real-world incidents often involve multiple authorization failures across the same API surface. In 2025, a vulnerability chain in ZITADEL’s Admin API (CVE-2025-27507) allowed authenticated low-privilege users to manipulate LDAP authentication settings and other sensitive configuration. The issue stemmed from insufficient authorization checks across multiple admin endpoints, combining object-level and function-level authorization gaps in a single attack surface.

Testing for BOLA vs BFLA: Different methodology, same authenticated scanner

Testing API authorization requires simulating how different users interact with the same system.

What BOLA testing requires

• Multiple users at the same privilege level
• Cross-session substitution of object identifiers
• Validation that users cannot access each other’s data

What BFLA testing requires

• Multiple roles with different permissions
• Attempts to access restricted endpoints
• Systematic testing of all HTTP methods

The combined testing matrix

Each row in the table below represents a concrete test case combining user role, request scenario, and expected authorization outcome. 

Given that most API attacks originate from authenticated sessions, multi-user and multi-role testing is essential. Authentication alone does not prevent abuse – it enables it when authorization is weak.

Why Invicti tests both for BOLA and BFLA

Invicti’s API DAST scanner tests both layers in a single workflow:

• Multi-session testing to detect BOLA
• Multi-role testing to detect BFLA
• Proof-based validation to confirm exploitability

This ensures teams focus on real, exploitable risk rather than theoretical findings.

BOLA and BFLA prevention: Different patterns for each vulnerability

In practice, effective API security requires both layers to be implemented together. Object-level authorization controls which data a user can access, while function-level authorization controls what actions they are allowed to perform.

These controls are often owned by different teams. Object-level authorization is typically implemented in backend data access code, while function-level authorization is enforced in middleware or API gateways. When these responsibilities are split, gaps emerge – one layer is implemented correctly while the other is overlooked.

A single endpoint can require both layers of protection. Function-level checks verify that a user is allowed to perform an action, while object-level checks ensure they are acting on the correct data.

BOLA prevention

This example shows how object-level authorization is enforced directly in the data query:

order = Order.objects.get(id=order_id, user=request.user)

By including the current user in the query, the application ensures that only objects owned by that user can ever be retrieved.

To prevent BOLA in APIs, object-level authorization must be enforced at the data layer by scoping queries to the current user or tenant.

Common failures include:

• Fetching objects by ID without user context
• Performing checks after data retrieval
• Relying on client-side validation

BFLA prevention

This example shows how function-level authorization is enforced before the endpoint logic runs:

@require_role('admin')
def delete_user(request, user_id):

The decorator blocks access unless the user has the required role, preventing unauthorized function execution.

Function-level authorization must be enforced before execution, typically through middleware or decorators tied to roles.

Common failures include:

• Missing role checks on specific endpoints
• Inconsistent enforcement across HTTP methods
• Allowing sensitive fields to be modified without restriction

Test your APIs for both BOLA and BFLA – and more

BOLA and BFLA are two sides of the same problem: incomplete authorization. Testing for only one leaves critical gaps, and manual approaches rarely cover both dimensions consistently.

Invicti’s API DAST scanner tests object-level and function-level authorization in a single authenticated API testing workflow. By combining multi-user and multi-role testing with proof-based validation, it confirms which vulnerabilities are really exploitable – not just theoretically possible.

This allows security and development teams to focus on fixing verified issues, reduce false positives, and ensure authorization controls are enforced across both data access and function execution.

See how Invicti helps you discover APIs and test API authorization end-to-end – request a demo to see modern API DAST in action.