OWASP API Security Top 10: A Practical Testing Guide

Change one number in a URL, from your own order ID to someone else’s, and if the API hands back their order anyway, you’ve just found the single most common API vulnerability in production today. No exploit code, no clever payload, just a request that should have been rejected and wasn’t.

That’s Broken Object Level Authorization, the first entry on the OWASP API Security Top 10, and it’s a useful reminder that most API breaches aren’t sophisticated. They’re missing checks.

This guide walks through all ten categories, what each one actually means, a realistic attack example, and a concrete way to test for it.

Quick Answer

The OWASP API Security Top 10 is a ranked list of the ten most critical API-specific security risks, maintained separately from the general OWASP Top 10 for web applications. The current edition is 2023, and it covers risks like Broken Object Level Authorization, Broken Authentication, and Server-Side Request Forgery, each requiring its own specific testing approach beyond what a generic security scan catches.

Key Takeaways

• The OWASP API Security Top 10 is a separate project from the general OWASP Top 10, don’t confuse the two when mapping a testing program or an audit requirement.
• The current API list is still the 2023 edition, the general OWASP Top 10 moved to a 2025 edition, but the API-specific list has not been updated since 2023.
• Most of these risks are logic flaws, missing authorization checks, exposed internal fields, that automated scanners typically miss entirely.
• Real-world API attack data shows most exploited vulnerabilities are fast, trivial, and remotely exploitable, not sophisticated.

What Is the OWASP API Security Top 10?

The OWASP API Security Top 10 is a standard awareness document ranking the ten most critical security risks specific to APIs, maintained separately from OWASP’s general web application Top 10. It focuses on risks unique to how APIs are designed and consumed, like broken object-level authorization and excessive data exposure, rather than general web vulnerabilities.

OWASP API Top 10 vs. the General OWASP Top 10: Don’t Confuse the Two

This matters more than it sounds like it should. OWASP maintains multiple Top 10 lists, and the general web application list and the API-specific list are entirely separate documents with different update cycles.

The general OWASP Top 10 was updated to its 2025 edition, finalized in early 2026. The API Security Top 10, by contrast, is still on its 2023 edition, OWASP has not published a newer API-specific revision. If a requirement, an RFP, or a client asks for “OWASP Top 10 compliance” for an API, confirm which list they actually mean before mapping your testing program to it.

The OWASP API Security Top 10 (2023), Explained

Each category below includes what it means, how it’s typically exploited, and how to test for it directly.

API1:2023 Broken Object Level Authorization (BOLA)

What it is: An API endpoint fails to verify that the requesting user actually owns or has permission to access the specific object being requested.

Attack example: A user changes an order ID in a request URL from their own to someone else’s and receives that person’s full order details.

How to test it: Authenticate as two different users with different permission levels, then attempt to access each other’s resources by directly manipulating object IDs in requests.

API2:2023 Broken Authentication

What it is: Weaknesses in how an API verifies identity, including weak token generation, missing token expiration, or flawed password reset flows.

Attack example: An attacker exploits a predictable or non-expiring authentication token to impersonate a legitimate user indefinitely.

How to test it: Review token generation for predictability, confirm tokens expire and can be revoked, and test authentication flows for logic flaws like password reset endpoints that don’t properly validate ownership.

Testvox worked through several of these exact authentication edge cases in an API authentication integration testing engagement, where token handling needed far more scrutiny than a surface-level login test would catch.

API3:2023 Broken Object Property Level Authorization

What it is: An API exposes or allows modification of object properties that a user shouldn’t be able to see or change, even if object-level access is otherwise correctly restricted.

Attack example: A user updates their own profile but includes an “isAdmin” field in the request body that the API accepts without checking whether they should be allowed to set it.

How to test it: Inspect full API responses for fields that shouldn’t be exposed to the current user, and attempt to modify fields in request payloads that shouldn’t be user-editable.

API4:2023 Unrestricted Resource Consumption

What it is: An API doesn’t limit how much of a resource, requests, data volume, or computation, a single user or client can consume.

Attack example: A single account sends an excessive volume of requests or requests unusually large data exports, degrading service for everyone else or running up infrastructure costs.

How to test it: Test for rate limiting on sensitive endpoints, attempt unusually large payload sizes or bulk requests, and confirm limits exist on pagination size and file uploads.

API5:2023 Broken Function Level Authorization

What it is: An API fails to properly restrict access to administrative or privileged functions based on user role.

Attack example: A regular user discovers and successfully calls an admin-only endpoint simply because the API didn’t check their role before executing it.

How to test it: Map every available endpoint, including undocumented ones found through API exploration, and attempt to call administrative functions using a standard, non-privileged account.

API6:2023 Unrestricted Access to Sensitive Business Flows

What it is: An API exposes a legitimate business function in a way that can be abused at scale, even though the function itself isn’t technically broken.

Attack example: An attacker automates a ticket-purchasing or coupon-redemption endpoint to buy far more than any real user reasonably would, exhausting inventory or abusing a promotion.

How to test it: Identify business-critical flows, purchases, redemptions, applications, and test whether they can be automated or repeated at a volume that creates real business harm.

API7:2023 Server Side Request Forgery (SSRF)

What it is: An API accepts a user-supplied URL or resource reference and fetches it without validating the destination, allowing an attacker to reach internal systems the API server can access.

Attack example: An attacker submits an internal cloud metadata URL instead of an expected external resource, tricking the API into leaking internal infrastructure credentials.

How to test it: Identify any endpoint that fetches a resource based on user input, and test whether it can be pointed at internal addresses, localhost, or cloud metadata endpoints.

API8:2023 Security Misconfiguration

What it is: Insecure default settings, incomplete configurations, overly permissive CORS policies, or unnecessary features left enabled in production.

Attack example: An overly permissive CORS configuration allows a malicious website to make authenticated requests to the API on a victim’s behalf.

How to test it: Review CORS policies, confirm unnecessary HTTP methods and debug endpoints are disabled in production, and check that security headers and TLS configurations follow current best practices.

API9:2023 Improper Inventory Management

What it is: Outdated, undocumented, or forgotten API versions and endpoints remain live and accessible, often with weaker security controls than the current version.

Attack example: An attacker discovers a deprecated v1 endpoint still running in production, lacking the authentication improvements added to the current version.

How to test it: Inventory every API version and environment actually running, not just the ones documented, and confirm deprecated versions are either properly secured or fully decommissioned.

API10:2023 Unsafe Consumption of APIs

What it is: An application trusts data from third-party APIs without the same validation it would apply to user input, assuming external APIs are inherently safe.

Attack example: A compromised or malicious third-party API returns unexpected data that gets processed without validation, leading to downstream injection or logic errors.

How to test it: Treat every third-party API response as untrusted input, test how your system handles malformed, unexpected, or oversized responses from external APIs you depend on.

None of these ten risks require exotic exploit techniques. Nearly all of them come down to a check that was assumed instead of enforced.

Automated Scanning vs. Manual Testing for These Risks

Automated scanners are genuinely useful for some of these categories, security misconfiguration and known vulnerable dependencies especially. They are far less effective against logic-based risks like BOLA or broken function-level authorization, since detecting those requires understanding what a user should be allowed to do, not just scanning for known vulnerability signatures.

This gap matters more than it used to. Recent industry attack data found that a notable share of all published vulnerabilities in 2025 were API-related, with the vast majority exploitable through a single, simple request rather than a sophisticated attack chain. Logic abuse and trust failures, not traditional code defects, are increasingly what attackers actually use.

That combination, simple to exploit, hard for a scanner to catch, is exactly why manual, role-based testing against each of these ten categories still matters.

Building an OWASP-Aligned API Testing Program

Treating this list as a one-time audit checklist undersells what it’s actually useful for. A properly built program tests against all ten categories on an ongoing basis, not just before a single compliance deadline.

1. Map your full API surface first. You can’t test what you don’t know exists, including undocumented or internal-only endpoints.
2. Test with multiple user roles. Several of these categories only reveal themselves when testing as a lower-privileged user attempting higher-privileged actions.
3. Automate what scanners can catch, manually test what they can’t. Reserve manual testing time for the logic-based categories scanners consistently miss.
4. Re-test after every significant API change. New endpoints and modified business logic reintroduce these risks regularly, not just once at launch.

Building and maintaining a program like this is exactly the kind of structured work covered under dedicated API testing services, where mapping risk to actual test coverage takes more than running a single scan before release.

Common Mistakes When Testing Against the OWASP API Top 10

• Relying solely on automated scanning. Most of these categories are logic flaws, not signature-based vulnerabilities a scanner is built to detect.
• Testing only with an admin account. Several categories only surface when testing as a standard user attempting to exceed their own permissions.
• Treating this as a pre-launch checklist only. New endpoints and features reintroduce these risks continuously, not just at initial release.
• Confusing this list with the general OWASP Top 10. Mapping a compliance requirement to the wrong document means testing the wrong things entirely.

Testvox has also covered broader API security testing practices in this practitioner’s guide to testing APIs securely, which pairs well with the category-specific detail here.

Most API breaches aren’t the result of a brilliant attacker. They’re the result of a check that should have existed and didn’t, exactly what each of these ten categories is designed to catch before an attacker finds it first. Structured, role-based testing against this list is exactly the kind of security discipline Testvox builds into API testing programs for growing engineering teams.

Frequently Asked Questions

What is the OWASP API Security Top 10?

It’s a standard awareness document, maintained by OWASP, ranking the ten most critical security risks specific to APIs, including broken authorization, broken authentication, and server-side request forgery, kept separate from OWASP’s general web application Top 10.

How is the OWASP API Security Top 10 different from the general OWASP Top 10?

The general OWASP Top 10 covers web application security risks broadly and was updated to a 2025 edition. The API Security Top 10 is a separate project focused specifically on API risks, and it remains on its 2023 edition with no newer API-specific revision published.

What is Broken Object Level Authorization (BOLA)?

BOLA occurs when an API fails to verify that a requesting user actually has permission to access a specific object, allowing someone to view or modify another user’s data simply by changing an ID in a request.

How do you test for Server-Side Request Forgery (SSRF) in APIs?

Identify any endpoint that fetches a resource based on a user-supplied URL or reference, then test whether it can be redirected toward internal addresses, localhost, or cloud metadata endpoints that shouldn’t be reachable externally.

Is the OWASP API Security Top 10 still current in 2026?

Yes. The 2023 edition remains the current and only published version of the API-specific list as of now. It’s separate from the general OWASP Top 10, which did receive a 2025 update.

Ready to Test Against the Full OWASP API Top 10?

Knowing the list is one thing. Systematically testing every category against your actual API, with the right user roles and real attack scenarios, is another. Talk to our API security testing team about building a program that covers all ten.