APIs fail differently from traditional web applications, and the security community built a dedicated reference to reflect that: the OWASP API Security Top 10. It is the standard checklist for the risks that actually break APIs in the wild. If you build, secure, or test APIs, it is worth understanding what each category means and why the list looks the way it does, because one theme dominates it, and that theme is where most real breaches live.
Why APIs needed their own list
The general OWASP Top 10 covers web applications broadly, but APIs have distinct failure modes. They expose data and operations directly to clients, they are consumed by code rather than people, and their security rests overwhelmingly on authorization decisions made on every request. The API-specific list captures those realities. Notice as you read how many entries are really about authorization, that is the signal that matters.
The categories, in plain terms
Broken Object Level Authorization (BOLA). The API verifies you are logged in but not that the specific record you requested belongs to you. Change an ID in the request, read someone else’s data. It sits at the top of the list because it is both endemic and high-impact, and because scanners miss it, the malicious request looks completely valid.
Broken Authentication. Weaknesses in how the API confirms identity: guessable or poorly validated tokens, missing revocation, tokens that survive a password reset, or endpoints that skip authentication entirely. Break this and everything downstream falls.
Broken Object Property Level Authorization. A finer-grained cousin of BOLA. The caller can read or modify object fields they should not, either seeing sensitive properties in a response or writing to fields they should never control (mass assignment).
Unrestricted Resource Consumption. No limits on requests or on expensive operations, enabling brute force, enumeration, denial of service, and runaway cost. Rate limiting is the direct defense.
Broken Function Level Authorization. Regular users reaching privileged or administrative functions because the endpoint was hidden rather than access-controlled. Hiding a function is not protecting it; the server must check privilege on every call.
Unrestricted Access to Sensitive Business Flows. Legitimate workflows, purchasing, booking, posting, abused through automation at a scale the business never anticipated: bots buying all the inventory, mass account creation, spam. The individual requests are valid; the volume and intent are the attack.
Server Side Request Forgery (SSRF). The API fetches a remote resource from a client-supplied URL without validating it, letting an attacker make the server reach internal systems it should not.
Security Misconfiguration. The broad category: default settings, unnecessary features left on, missing hardening, verbose errors that leak internal detail, permissive CORS. Individually minor, collectively a wide-open door.
Improper Inventory Management. You cannot protect endpoints you have forgotten. Undocumented, deprecated, or “shadow” APIs still serving traffic are a favorite target because nobody is watching them. An accurate inventory is a security control.
Unsafe Consumption of APIs. Your API trusts data from third-party APIs it consumes without validating it, inheriting their weaknesses. Trust from an external source is not a reason to skip validation.
The theme you cannot miss
Read the list and one pattern is unmistakable: authorization failures dominate. Several of the top categories are variations on the same root problem, the API does not correctly verify that this caller may access this thing. That is the defining API vulnerability, and it is exactly what automated tools are worst at finding, because every exploiting request is technically valid.
This is why authorization deserves the center of your API security effort: enforce it on every request, for every object and every function, and never trust an identifier from the client as proof of ownership.
Using the list
The Top 10 is most valuable as a shared language and a testing map. For development, it is a checklist of what to get right, above all, rigorous per-object and per-function authorization. For testing, it structures a real assessment: a thorough API penetration test works through these categories deliberately, and because the highest-ranked risks are authorization flaws invisible to scanners, it takes a skilled human testing with multiple accounts to prove them.
The OWASP API Security Top 10 endures because it names what actually goes wrong. Treat it as both a design guide and a testing agenda, and put authorization at the top of your attention, just as the list does. To see how your own APIs hold up against it, scope an assessment.
Written by
Invadel Team
Senior penetration testers writing from real engagements — the same team that scopes, tests, and reports for our clients. About Invadel →