What is an API Security Audit?

What is an API security audit?

An API security audit is a structured review of an API's design, implementation and configuration against a defined set of security requirements, to find weaknesses before an attacker does. It combines an inventory of endpoints, automated scanning and manual testing, and ends in a prioritised list of findings with fixes and a re-test.

The terms overlap in practice. A scan is automated and finds known issue classes. A penetration test tries to exploit weaknesses. An audit checks the API against a stated standard and usually uses both, plus a look at design, configuration and documentation. Agree on scope and wording with whoever you hire or ask.

The standards an audit checks against

Most audits start from the OWASP API Security Top 10 (2023), an awareness list of the most critical API risks:

1. API1:2023 Broken Object Level Authorization
2. API2:2023 Broken Authentication
3. API3:2023 Broken Object Property Level Authorization
4. API4:2023 Unrestricted Resource Consumption
5. API5:2023 Broken Function Level Authorization
6. API6:2023 Unrestricted Access to Sensitive Business Flows
7. API7:2023 Server Side Request Forgery
8. API8:2023 Security Misconfiguration
9. API9:2023 Improper Inventory Management
10. API10:2023 Unsafe Consumption of APIs

For a deeper checklist, the OWASP Application Security Verification Standard (ASVS, version 5.0.0 published 30 May 2025) lists security requirements and is meant as a basis for testing web application technical security controls. The OWASP Web Security Testing Guide covers how to test them. Our top API security risks entry explains the risks themselves, and API security covers the wider topic.

An example: broken object level authorization

OWASP's own scenario for API1 is an e-commerce API with an endpoint like /shops/{shopName}/revenue_data.json. An attacker gets the list of shop names from another endpoint and swaps each one into the URL. If the server checks only that the caller is logged in, not that they own that shop, the script reads the revenue of thousands of stores. A scanner rarely spots this, because every response is a valid 200. An auditor tests it by calling the endpoint as one user with another user's identifiers. The fix is an ownership check on every function that takes a client-supplied ID.

How an audit unfolds

1. Scope and inventory. List every API and version: OpenAPI files, gateway logs, code and traffic. See API discovery and API sprawl. You cannot audit an endpoint nobody knows exists.
2. Pick the standard. OWASP API Top 10, ASVS or your own policy.
3. Automated scan. Run a scanner against a test environment to cover known issue classes quickly.
4. Manual testing. Authorization flaws need real test accounts with different roles, so the auditor can ask "can user A reach user B's data?".
5. Triage. Rate each finding by impact and ease of exploitation, and assign owners.
6. Fix and re-test. Confirm the fix closed the issue and did not break something else.
7. Report. Findings, evidence, severity and remediation, with a short summary for non-engineers.

What gets checked

• Authentication: token validation, expiry, credential handling, protection against brute force.
• Authorization: checks at object, property and function level on every endpoint, not just at the login screen.
• Input handling: injection, request size limits, schema validation, server-side requests built from user input.
• Resource limits: rate limits, pagination caps, expensive operations.
• Data exposure: fields returned that the caller should not see, tokens or personal data in logs, error messages that leak internals.
• Configuration: transport encryption, CORS, debug modes, default credentials.
• Inventory and third parties: forgotten old versions, and how the API handles data from other APIs it calls.

Common mistakes

• Auditing only the documented endpoints. Old versions and undocumented routes are where the surprises are.
• Testing with one admin account. Authorization bugs only show up when you switch identities.
• Rate limits only at the gateway. If the origin can be reached directly, the limit does nothing.
• A one-off audit. The API changes every sprint, so a clean report ages quickly.
• Scanning without permission or on production. Get written authorisation, and prefer a test environment. See the penetration testing tools comparison.
• No re-test. A finding is closed when it is verified, not when a ticket is.

How it relates to monitoring and load testing

LoadFocus is not a security auditor and does not scan for vulnerabilities. What it can do is keep watching behaviour after an audit has fixed something. API monitoring runs scripted checks on a schedule (every 5 minutes on the free plan) from several of its 25 regions and can assert on status code, body and headers, so a check that expects a request without a token to be refused will fail if a later deploy opens it up. Multi-step checks can chain requests, for example to log in and then call another endpoint. For resource consumption, a free API load test shows how a public endpoint behaves under volume (GET requests only, up to 25 virtual users from one location), and you should only load test systems you own or have permission to test. For deeper hunting on live traffic, see API threat hunting.

FAQ: API Security Audits

How often should an API be audited?

Before launch, after major changes to authentication or data handling, and on a regular schedule after that. Because APIs change constantly, many teams add automated checks between full audits instead of relying on one report a year.

What is the difference between an API security audit and a penetration test?

The words overlap. A penetration test focuses on trying to exploit weaknesses and often covers more than the API. An audit checks against a stated standard and covers design, configuration and process as well as exploitability. Confirm what each engagement includes before it starts.

Do internal-only APIs need an audit?

Yes. Internal APIs are reachable by anyone who gets a foothold inside the network or a compromised service, so they deserve the same authentication, authorization and logging as public ones.

What should we prepare for an audit?

Current API specifications, an inventory of endpoints and versions, test accounts for each role, a test environment, and a list of known issues. The more complete the inventory, the less time goes to discovery.

Can an automated scanner replace an audit?

No. Scanners cover known issue classes quickly, but they do not know who should own which object, so flaws such as broken object level authorization usually need manual testing with several identities.