Broken Object Level Authorization (BOLA) occurs when a REST API exposes an object identifier—such as an account, transaction, or loan ID — without verifying whether the authenticated user is authorized to access that specific resource.
To protect fintech REST APIs, implement server-side authorization checks for every object request, validate permissions using the user's authenticated context and resource ownership, and avoid relying on client-supplied IDs alone. Using unpredictable identifiers such as UUID v4 or ULIDs can reduce object enumeration, but they should be treated as an additional security layer—not a replacement for authorization.
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