Top 10 API Vulnerabilities in 2026

APIs have become the dominant attack surface in modern web applications. They expose business logic directly, often with weaker controls than traditional web interfaces.

The OWASP API Security Top 10 is the go-to reference — here's a practitioner's take on what actually shows up in real-world pentests in 2026.

1. BOLA — Broken Object Level Authorization

Still number one, and for good reason. BOLA (also called IDOR) occurs when an API endpoint accepts user-supplied identifiers and returns data without verifying that the requesting user is actually authorized to access it. A request like GET /api/invoices/4821should check whether invoice 4821 belongs to the authenticated user. Many don't.

Detection: enumerate object IDs across endpoints. Swap your ID for another user's. If the server returns data, it's vulnerable.

2. Broken Authentication

Weak token validation, missing expiry on JWTs, predictable reset tokens, and lack of brute-force protection on login endpoints. In 2026, the most common variant we encounter is JWT algorithm confusion — accepting alg: none or switching RS256 to HS256 and signing with the public key.

3. Broken Object Property Level Authorization

Related to BOLA, but at the property level. An endpoint that correctly checks whether you can access object X might still return sensitive fields you shouldn't see — internal IDs, admin flags, other users' emails. Or accept properties in a PATCH request that should be read-only (the mass assignment variant).

4. Unrestricted Resource Consumption

No rate limiting, no request size limits, no query depth limits on GraphQL endpoints. These lead to DoS conditions, excessive cloud costs, and in some cases allow attackers to enumerate large datasets cheaply. Especially relevant for AI-powered features where each request triggers expensive model inference.

5. Broken Function Level Authorization (BFLA)

While BOLA is about accessing another user's object, BFLA is about accessing administrative functions. The classic example: a regular user sending a DELETE request to an admin-only endpoint and it working because the UI hides the button but the API doesn't enforce the role check.

6. Unrestricted Access to Sensitive Business Flows

Automatable flows that should have human friction: account creation for spam, coupon code redemption loops, voting manipulation. These aren't classic vulnerabilities — they're business logic flaws that require understanding the application's intended behavior.

7. Server-Side Request Forgery (SSRF)

Any endpoint that fetches a URL provided by the user is a potential SSRF vector. In cloud environments, SSRF can expose instance metadata endpoints (AWS IMDSv1, GCP metadata) and lead to credential theft. Webhooks, PDF generators, and link previews are the most common sources.

8. Security Misconfiguration

Permissive CORS headers (Access-Control-Allow-Origin: *), debug endpoints left exposed in production, verbose error messages leaking stack traces and internal paths, HTTP methods not restricted, default credentials on backend services. All still rampant.

9. Improper Inventory Management

Shadow APIs — old API versions (/v1, /v2) that were never properly deprecated and still work, often with weaker security controls than the current version. Also includes undocumented endpoints that show up in JavaScript bundles or mobile app decompilation.

10. Unsafe Consumption of APIs

APIs that blindly trust data from third-party services and process it without validation. If your API fetches data from a partner's API and renders it without sanitization, an attacker who compromises that partner (or can influence the data) can attack your users. Trust boundaries between services are often overlooked.

IntrudR automatically tests for all 10 of these vulnerability classes during a scan. Start a free scan →