API Security in 2026: How to Protect Your APIs from the Top 10 Threats

APIs are the connective tissue of modern software. Every mobile app, every single-page application, every microservice, and every integration between systems communicates through APIs. This makes APIs the largest and most exposed attack surface in most organizations. According to Gartner, API attacks are the most frequent attack vector for web applications, and the trend is accelerating.

The OWASP API Security Top 10 provides a framework for understanding the most critical API security risks. This guide goes beyond listing the risks — it provides practical, implementable solutions for each one, with code examples and configuration guidance.

Broken Object-Level Authorization (BOLA)

BOLA is the number one API security risk because it is both common and easy to exploit. It occurs when an API endpoint accepts an object identifier (user ID, order ID, file ID) from the client and does not verify that the authenticated user has permission to access that specific object.

The classic example: an API endpoint GET /api/orders/123 returns order details. An attacker changes the ID to /api/orders/124 and receives another user's order — including their personal information, payment details, and purchase history. The API authenticated the user but did not check whether that user owns order 124.

Fix this by implementing authorization checks at the data access layer, not just the endpoint level. Every database query should include a filter for the authenticated user's ID. Use middleware that automatically scopes queries to the authenticated user. And replace sequential IDs with UUIDs to prevent enumeration attacks — changing from /orders/123 to /orders/550e8400-e29b-41d4-a716-446655440000 does not fix the authorization bug, but it makes it much harder for attackers to guess valid IDs.

Broken Authentication

Authentication failures allow attackers to impersonate legitimate users. Common causes include weak password requirements, missing brute-force protection, JWT tokens that do not expire, sensitive credentials in URLs, and authentication endpoints that do not implement rate limiting.

Implement robust authentication: use bcrypt or Argon2 for password hashing (never MD5 or SHA), issue short-lived JWTs (15 minutes for access tokens, 7 days for refresh tokens), implement account lockout after 5 failed attempts, use HTTPS exclusively for all authentication endpoints, validate JWT signatures on every request, and implement token revocation for logout and compromised accounts.

Consider moving to passwordless authentication using passkeys (WebAuthn). Passkeys eliminate password-related vulnerabilities entirely — no passwords to steal, no credentials to phish, and no brute-force attacks possible.

Broken Object Property-Level Authorization

APIs often return more data than the client needs, exposing sensitive fields that should be restricted. An API returning user profiles might include internal fields like isAdmin, passwordHash, or internalNotes that the frontend never displays but an attacker can see in the API response.

Similarly, mass assignment vulnerabilities occur when APIs accept and process fields that should not be user-modifiable. A user update endpoint that blindly applies all submitted fields could allow an attacker to set isAdmin: true in their update request.

Fix this with explicit response serialization — define exactly which fields are included in API responses for each endpoint and user role. Use allowlists for accepted input fields rather than blocklists. Never expose internal implementation details (database IDs, internal status codes, system paths) in API responses.

Unrestricted Resource Consumption

APIs that do not limit resource consumption are vulnerable to denial-of-service attacks and cost-based attacks (running up your cloud bill). Implement rate limiting at multiple levels: per-user (100 requests per minute for authenticated users), per-IP (50 requests per minute for unauthenticated requests), and per-endpoint (expensive operations like file uploads get lower limits).

Set payload size limits — reject requests with bodies larger than necessary. Implement pagination for list endpoints — never return unbounded result sets. Set timeouts for long-running operations and limit the complexity of queries (depth limiting for GraphQL, JOIN limits for SQL-backed endpoints).

Broken Function-Level Authorization

Administrative functions that are accessible to regular users represent one of the most critical API vulnerabilities. This often happens when different user roles access the same API with different UI views — the frontend hides the admin buttons, but the API endpoints are still accessible to anyone with a valid token.

Implement role-based access control (RBAC) with server-side enforcement. Never rely on client-side UI restrictions for security. Use middleware that checks the user's role before executing any endpoint handler. Implement the principle of least privilege — start with no permissions and explicitly grant only what each role needs.

Server-Side Request Forgery (SSRF)

SSRF occurs when an API fetches a URL provided by the user without proper validation. An attacker can make the API server request internal resources (like metadata services on cloud providers), scan internal networks, or access services that are not exposed to the internet.

Validate and sanitize all user-supplied URLs. Maintain an allowlist of permitted domains. Block requests to private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) and cloud metadata endpoints (169.254.169.254). Use a dedicated network segment for external requests with no access to internal services.

Security Misconfiguration

Default configurations are almost always insecure. Common misconfigurations include CORS headers set to allow all origins, verbose error messages that expose stack traces and internal paths, default credentials on API gateways and management interfaces, unnecessary HTTP methods enabled (DELETE on read-only resources), and missing security headers (Content-Security-Policy, X-Content-Type-Options, Strict-Transport-Security).

Automate configuration security checks in your CI/CD pipeline. Use infrastructure as code to ensure consistent, secure configurations across all environments. Conduct regular security configuration audits and compare your settings against security benchmarks like CIS (Center for Internet Security).

Inventory Management and Documentation

You cannot secure APIs you do not know about. Shadow APIs — undocumented endpoints created during development and never decommissioned — are common attack targets because they are often forgotten and unmaintained.

Maintain a comprehensive API inventory. Use OpenAPI (Swagger) specifications to document every endpoint. Implement API gateways that reject requests to undocumented endpoints. Conduct regular API discovery scans to identify shadow APIs. Decommission deprecated API versions promptly — old versions often lack the security improvements of newer versions.

Building an API Security Program

API security is not a one-time effort — it is an ongoing program. Include API security testing in your CI/CD pipeline, conduct quarterly API security reviews, train developers on secure API development practices, and monitor API traffic for anomalous patterns that could indicate attacks or data exfiltration.

ZeonEdge provides API security audits, penetration testing, and secure API development consulting. Protect your APIs with ZeonEdge.