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Secure a web API by verifying identity, checking authorization for every object, action, and property, limiting resource and business-flow abuse, constraining outbound requests, and keeping configuration, integrations, and deployed versions under control. Treat the OWASP API Security Top 10 2023 as an API-specific review framework—not a statistically proven ranking or a complete security standard—and pair it with broader application security work.
Start with identity, authorization, and a threat model
Authentication answers “who or what is calling?” Authorization answers “what may that caller do?” They are separate checks: a valid identity does not automatically have permission to read a particular record, change a particular field, or invoke an administrative operation.
Before implementation or review, define security requirements for the API’s data, users, operations, integrations, and deployment. OWASP recommends repeatable security processes informed by a project’s needs; its API-specific list complements rather than replaces broader application security work. See the OWASP guidance for developers.
Use the OWASP API Security Top 10 as a review map
The OWASP API Security Top 10 2023 names ten API risk categories. Turn each into a testable question for your own system rather than treating the sequence as a universal prevalence ranking.
#1 Best Overall
| Risk (2023) | Review question | What to verify |
|---|---|---|
| API1: Broken Object Level Authorization | Can a caller access only the specific object they are entitled to? | For each request that names an object, verify permission for the authenticated identity against that object. Test requests using identifiers belonging to other users or tenants. |
| API2: Broken Authentication | Can an attacker misuse or obtain a valid identity or token? | Review token and identity flows, how credentials are handled, and whether authentication failures expose or permit misuse of credentials. |
| API3: Broken Object Property Level Authorization | Can a caller read or change only the properties they are allowed to? | Explicitly control which fields can be returned and which can be supplied for changes. Do not rely on hiding a field in the user interface. |
| API4: Unrestricted Resource Consumption | Can requests exhaust technical or paid resources? | Put limits and safeguards around resource-intensive operations; consider the resources consumed by each endpoint and request pattern. |
| API5: Broken Function Level Authorization | Can a caller invoke an operation outside their role or permission? | Check authorization for the requested function, including privileged operations, not just whether the caller has authenticated. |
| API6: Unrestricted Access to Sensitive Business Flows | Can automation abuse a legitimate business process? | Identify sensitive or automatable flows such as purchases or posting, then add safeguards suited to the harm that repeated or automated use could cause. |
| API7: Server Side Request Forgery | Can user input cause the server to fetch an unintended remote resource? | Validate and constrain user-supplied remote resource addresses and review which destinations the service can reach. |
| API8: Security Misconfiguration | Are deployed services configured safely? | Review production configuration and exposed debug or other unintended surfaces; apply secure configuration consistently. |
| API9: Improper Inventory Management | Do you know every deployed API host and version? | Maintain an inventory of hosts and deployed versions so older or forgotten interfaces do not escape review and protection. |
| API10: Unsafe Consumption of APIs | Is data from integrated APIs treated as untrusted? | Validate and handle third-party API responses as untrusted input, even when they come from a known integration. |
These category names and risk areas come from the OWASP API Security Top 10 2023. OWASP describes the list as an awareness resource. Its methodology says the public call for data did not produce data suitable for relevant statistical analysis of the most common API security issues; the edition reviewed publicly available incident material from 2019–2022 and used specialist input and team consensus for prevalence ratings. Use it to organize review, not to claim that its order measures the risk in your environment. The API list also does not cover every generic application risk, such as injection and vulnerable components.
Check authorization at the object, function, and field levels
Authorization checks should be tied to the requested operation and data, not merely to a route or a successful login. For each endpoint, identify the caller, the object being accessed, the action being performed, and the input or output properties involved. Then test whether the same request is correctly restricted for a caller with a different role, tenant, or ownership relationship.
- Object: Can this identity access this exact record?
- Function: Can this identity perform this exact operation?
- Property: Can this identity read or modify each field involved?
Apply those checks to both reads and writes. A caller may be allowed to view an object without being allowed to change every property on it, and permission to use one operation does not imply permission to invoke another.
Rank #2
Protect OAuth flows without confusing authorization and identity
When OAuth 2.0 is in scope, follow current applicable standards and the OWASP OAuth 2.0 Protocol Cheat Sheet. OWASP recommends Authorization Code with PKCE, including for single-page and native applications, and advises binding protections to the transaction. The cheat sheet labels the implicit grant deprecated and says not to use it.
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PKCE protects the authorization code flow; it does not, by itself, address every risk to access or refresh tokens. Consider additional protections, such as sender-constrained tokens where they are supported and warranted. Keep the terminology precise: OAuth 2.0 is an authorization framework. OpenID Connect adds an identity layer on top of OAuth 2.0, allowing a client to verify an end-user identity based on authentication by an authorization server.
Limit resource use and abuse of legitimate business flows
An authenticated request can still be harmful. Identify endpoints that consume substantial compute, storage, bandwidth, or paid third-party resources, and establish limits and safeguards appropriate to their cost and impact. Separately review business processes that can be automated—such as purchases or posting—because technical rate controls alone may not address abuse of a valid workflow.
Choose controls based on the operation and its threat model. Review whether repeated requests, high-cost inputs, or automated sequences could exhaust resources or produce an unwanted business outcome. Avoid relying on a single generic request limit as the answer to both technical resource exhaustion and business-flow abuse.
Constrain server-side requests and secure integrations
If an API accepts a remote address or other input that leads the server to make a request, validate the destination and constrain where the service can connect. Review this at the point where the remote request is made; accepting a URL as syntactically valid does not establish that its destination is safe.
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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →For third-party API integrations, treat returned data as untrusted input and validate it before using it in later processing. Include integrated services in the threat model and review what happens when responses are malformed, unexpected, or fail to load. A trusted provider does not remove the need to handle its data safely.
Rank #4
Keep configuration, API versions, and hosts in view
Review the configuration of deployed services for unintended exposure, including debug surfaces that should not be available in production. Make configuration review part of release and operational processes rather than a one-time setup task.
Maintain an inventory of API hosts and deployed versions. Use it to identify interfaces that still need ownership, security review, and appropriate controls—including older versions that may remain reachable after a newer version launches.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Make security review repeatable
A useful review follows the API through design, implementation, integration, and deployment. Tie checks to documented requirements and repeat them when endpoints, permissions, dependencies, or deployment configurations change.
- Map the surface: List API hosts, versions, endpoints, identities, roles, objects, and third-party integrations.
- Define expected access: Record which identities may perform which operations on which objects and properties.
- Test abuse cases: Check object, function, and field authorization; resource exhaustion; automatable business flows; and user-controlled outbound requests.
- Review deployment and dependencies: Check production configuration, debug exposure, inventory accuracy, and validation of third-party responses.
- Repeat after changes: Re-run the relevant checks as part of the team’s security and release process.
OWASP also points developers to its developer resources, including the REST Security Cheat Sheet and intentionally vulnerable learning applications such as crAPI and Juice Shop. These can support learning and review practice; they do not establish that a particular API is secure.
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For a separate task—capturing a rendered page such as API documentation—ScreenshotNeo is a website screenshot API and MCP server. It is not an API security control, and using it does not replace the checks above. One GET request returns a screenshot or PDF; the API supports PNG, JPEG, or WebP output. The request below captures the ScreenshotNeo documentation page as a WebP image. See the ScreenshotNeo API docs for options.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://screenshotneo.com/docs/ -o shot.webp- Cookie and consent banners, newsletter popups, and chat widgets can be removed before capture; each step can be turned off.
- Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed; responses include X-Page-Verdict and X-Billed headers.
- An MCP server provides take_screenshot, get_page_info, and capture_pdf tools for AI agents and MCP clients.
- The free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000 screenshots.
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