BOLA vs BFLA: Understanding API Authorization Attacks

BOLA and BFLA sound similar. They both involve authorization failures. But they represent fundamentally different attack patterns, and they require different detection approaches.

BOLA: Accessing the Wrong Data

Broken Object Level Authorization (BOLA) occurs when an API validates that a user can perform an action, but not whether they can perform it on a specific resource.

The classic example:

GET /api/orders/12345   → Returns your order
GET /api/orders/12346   → Returns someone else's order

The API confirms you’re authenticated. It confirms you have permission to view orders. It never checks whether order 12346 belongs to you.

Why it’s pervasive: Developers often handle authorization at the route level (“users can access /orders”) rather than the object level (“users can access their own orders”). This gap is invisible in normal testing. You’d need to try accessing another user’s data to find it.

Real-world impact: BOLA vulnerabilities have exposed millions of records. Attackers simply iterate through IDs, scraping data they shouldn’t access.

BFLA: Accessing the Wrong Functions

Broken Function Level Authorization (BFLA) occurs when an API exposes administrative or privileged functions to regular users.

Examples:

Regular user discovers:
POST /api/admin/users           → Create any user
DELETE /api/users/{id}          → Delete any account
PUT /api/users/{id}/role        → Promote to admin

The API doesn’t properly restrict who can call sensitive endpoints. The functions exist, the attacker just needs to find and call them.

Why it happens: Different endpoints are built by different teams or at different times. Admin APIs are “internal.” Developers assume they’re not exposed. Frontend applications hide admin buttons, but the APIs remain accessible.

Common patterns: Changing HTTP methods (GET to DELETE), discovering /admin/ paths, modifying user role fields in update requests.

The Key Distinction

Think of authorization as two questions:

BOLA: “Can this user access this specific record?” Failure: User A accesses User B’s data through a valid endpoint.

BFLA: “Can this user call this function at all?” Failure: Regular user calls an admin-only endpoint.

BOLA is horizontal privilege escalation (same permission level, wrong data). BFLA is vertical privilege escalation (gaining higher permissions).

Detection Challenges

Both vulnerabilities are difficult to detect because the requests look legitimate.

BOLA detection signals:

Sequential ID access patterns: requests to /users/1, /users/2, /users/3 in rapid succession. High-frequency access to resources with different owners. Responses returning data for users other than the authenticated user.

BFLA detection signals:

Non-admin users calling admin endpoints. PUT/DELETE requests from accounts that typically only send GET requests. Requests to sensitive paths like /admin/, /internal/, /management/.

Neither attack involves malicious payloads. Traditional WAF signatures won’t catch them. Detection requires understanding the relationship between users and resources, context that only comes from analyzing traffic patterns.

Prevention Strategies

For BOLA:

Implement object-level authorization checks on every request. Don’t rely on obscure IDs. Attackers will enumerate them. Use indirect references that map to user-specific resources. Log and monitor access patterns.

For BFLA:

Define explicit role-based access control for every endpoint. Deny by default. Functions require explicit permission grants. Don’t assume endpoints are hidden. Audit admin functionality regularly.

Why Both Matter

BOLA lets attackers steal data horizontally across your user base. BFLA lets attackers take over your system entirely. Together, they represent the majority of API authorization breaches.

Detecting them requires visibility into who is accessing what, and whether those access patterns make sense. That’s not something you get from logs alone.

Detect Authorization Attacks Automatically

Cyron monitors API traffic for BOLA and BFLA patterns: sequential ID enumeration, privilege escalation attempts, and unauthorized function access. Get alerted before data leaves your system.