Module 8 · API Security (OWASP API Top 10)

Manish Garg
Manish Garg Associate of (ISC)² · RingSafe
Apr 19, 2026
12 min read
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Last updated: May 1, 2026

OWASP API Top 10 in practice, GraphQL testing, gRPC, SSRF, LLM-integrated API attacks. The 2026 API attack surface. Pro module.
🎯 WEB APP PENTEST PATH
HARD
🔐 PRO
⏱ 120 min
Module 8 of 8

What you’ll learn

  • The OWASP API Top 10 (2023, revised for 2025) in practical depth
  • Why APIs carry more commercial risk than UIs in 2026
  • REST vs GraphQL vs gRPC testing methodologies
  • SSRF, resource exhaustion, shadow APIs, and unsafe upstream consumption
  • LLM-integrated API testing — the new 2026 attack surface

Prerequisites: Modules 1–7.

In 2026, the API is the product. Modern web applications are thin clients (browser, mobile app, third-party integration) over APIs that carry all the business logic. This means APIs carry all the commercial risk — and in pentest findings, APIs produce the overwhelming majority of high-severity bugs.

Web pentesting that stops at the frontend misses most of the real vulnerabilities. This module covers the API-specific attack surface using the OWASP API Security Top 10 as the framework, with the 2026 additions that matter (LLM-integrated APIs, event-driven patterns, gRPC).

Why API testing differs from web-app testing

  • The UI hides most of the attack surface. An API has dozens of endpoints the frontend never hits.
  • Authorization bugs are more common and more severe in APIs.
  • Rate limiting and resource consumption issues are more impactful (cloud costs, DoS).
  • Multi-tenant boundary violations produce cleaner findings.
  • Supply-chain concerns — consuming third-party APIs introduces unsafe-consumption attack vectors.
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