Object level authorization decides whether a caller may access a specific record or resource instance, such as one order, document, or account. Function level authorization decides whether the caller may invoke a specific operation or endpoint, such as an admin-only action. Both are needed because attackers can exploit either missing resource checks or missing role checks.
How object level authorization and function level authorization differ
Object level authorization answers a narrower question: is this caller allowed to reach this specific resource instance? In API security, that means checking whether a user can read order 123, update account A, or delete document X. Function level authorization asks a different question: may this caller invoke the operation at all, such as an admin endpoint, bulk export action, or privilege-changing API call.
The distinction matters because both checks protect different layers of the API trust model. Object checks constrain access to data instances, while function checks constrain access to capabilities. An API can be strong on one and weak on the other, which is why broken object-level authorization and broken function-level authorization are treated as separate failure modes in API testing and review. OWASP API Security Top 10
Think of object level authorization as “which row, record, or resource may this identity touch?” and function level authorization as “which endpoint or action may this identity trigger?” A caller with valid authentication can still be stopped by either check, but for different reasons. One is about ownership or entitlement to a specific item, the other is about the authority to perform a sensitive operation.
Where API designs most often get this wrong
Object level authorization failures commonly appear when the API trusts a client-supplied identifier without revalidating ownership, scope, or tenancy. That is how an attacker can swap an ID in a URL or request body and reach another user’s data. Function level authorization failures usually appear when an endpoint is exposed to any authenticated caller even though the action should be limited to a smaller role, administrative workflow, or privileged service account.
The practical consequence is that an API can appear “secure” during normal usage while still allowing horizontal or vertical abuse. Object checks prevent one customer from reaching another customer’s records; function checks prevent a low-privilege caller from invoking sensitive capabilities that were never meant to be broadly available. Both need explicit enforcement because API routing, authentication, and UI restrictions do not provide them automatically. OWASP Web Security Testing Guide
In mature environments, these checks are usually implemented at the authorization layer, not in ad hoc controller logic alone. Object decisions often depend on ownership, tenant context, or scoped access rules. Function decisions often depend on role, policy, scope, or administrative approval. If those rules are inconsistent across services, the API becomes easy to misconfigure and hard to audit.
Practitioner guidance for testing and control design
What to verify: Test object and function controls separately. A request that passes authentication should still fail if the caller changes an object identifier they do not own, and it should also fail if the caller invokes an operation outside its role or scope.
Common mistake: Teams often assume role checks alone cover the API. They do not. A user can have a legitimate role and still reach the wrong object if instance-level checks are missing, so you need both entitlement to the action and authorization to the target resource.
What good looks like: Every sensitive endpoint has a clear rule for who may call it, and every object reference is checked against the caller’s allowed tenant, ownership, or scope before the response is returned or the mutation is applied.
Practitioner takeaway: Separate “may this caller do this operation?” from “may this caller do it to this specific resource?” and test both paths independently, because API breaches usually exploit the gap between them.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP API Security Top 10 addresses the attack and risk surface, while OWASP ASVS and NIST SP 800-53 Rev 5 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP API Security Top 10 | BOLA — Broken Object Level Authorization | Directly addresses unauthorized access to specific API objects or records. |
| BFLA — Broken Function Level Authorization | Directly addresses unauthorized invocation of sensitive API functions or endpoints. | |
| Recommendation — Enforce per-object authorization checks on every resource access and mutation. Restrict sensitive endpoints by role, scope, or policy before execution. | ||
| OWASP ASVS | V4 — Access Control | Access control verification covers both object and function authorization failures in application APIs. |
| Recommendation — Verify object and function authorization rules on all protected requests. | ||
| NIST SP 800-53 Rev 5 | AC-3 — Access Enforcement | Requires enforcing approved access decisions for subjects and protected resources. |
| AC-6 — Least Privilege | Function authorization should limit sensitive API operations to the minimum needed privileges. | |
| AU-2 — Event Logging | Authorization failures and sensitive API calls should be logged for detection and review. | |
| Recommendation — Apply access enforcement consistently at both the resource and operation layers. Limit privileged API actions to the smallest necessary set of callers. Log denied and privileged API actions for review and anomaly detection. | ||
Related resources from NHI Mgmt Group
- What is the difference between gateway controls and service-level authorization in API security?
- What is the difference between scope-based authorization and object-level authorization in MCP?
- What is the difference between authentication and externalized authorization in API security?
- What is the difference between broken object level authorization and broken object property level authorization?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on September 23, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
