The OWASP Top 10, Explained Simply (2026)

The OWASP Top 10 is a community-built list of the most critical web application security risks. It's the single best starting point for understanding where web apps actually break — and it's foundational knowledge for any pentester or developer.

Here's each category in plain words, with the defensive takeaway.

A01 — Broken Access Control

Users can do or see things they shouldn't (viewing another user's data, hitting admin functions). Defense: enforce authorization on the server for every request; deny by default.

A02 — Cryptographic Failures

Sensitive data is exposed because it wasn't encrypted properly (or at all). Defense: encrypt data in transit (TLS) and at rest; never roll your own crypto; don't store secrets you don't need.

A03 — Injection

Untrusted input is interpreted as a command — classic SQL injection, plus OS and other injections. Defense: parameterized queries, input validation, and safe APIs that separate code from data.

A04 — Insecure Design

The flaw is in the design, not a bug — missing rate limits, weak workflows. Defense: threat-model early; build security requirements in from the start.

A05 — Security Misconfiguration

Default passwords, verbose errors, unnecessary features left on. Defense: harden by default, remove what you don't use, and automate configuration.

A06 — Vulnerable and Outdated Components

Using libraries with known holes. Defense: inventory your dependencies, patch promptly, and track advisories (CVEs matter here).

A07 — Identification and Authentication Failures

Weak logins — credential stuffing, poor session handling. Defense: MFA, strong password policies, secure session management.

A08 — Software and Data Integrity Failures

Trusting code or updates that could be tampered with (supply-chain risk). Defense: verify signatures, secure your CI/CD pipeline.

A09 — Security Logging and Monitoring Failures

You can't respond to what you can't see. Defense: log security-relevant events, monitor them, and alert on anomalies.

A10 — Server-Side Request Forgery (SSRF)

The server is tricked into making requests to places it shouldn't. Defense: validate and allow-list outbound destinations; segment networks.

How testers use it

The Top 10 is a checklist mindset, not a recipe. A pentester maps each category to the target's real features and asks, "could this break here?" Modern AI-driven testing scales that questioning across an entire app quickly — then verifies what's actually exploitable rather than just flagging maybes.

Learn it properly

Each category deserves hands-on practice. Our free Pentevo Academy covers web app security and the OWASP risks as part of the full CEH path — with videos, examples and quizzes.