OWASP Top 10 for Beginners, Explained

The OWASP Top 10 is a widely used awareness list of the most critical security risks to web applications, published by the Open Worldwide Application Security Project. Developers use it to build safer software, and testers use it as a checklist. This guide follows the 2025 edition, the current one in October 2026. Check owasp.org for later updates; the core ideas change slowly.

A01Broken Access Control

Users can do things they should not be allowed to do. For example, changing a number in a web address to view another customer's invoice. Server-side request forgery (SSRF), where an attacker makes the server fetch internal addresses for them, is now counted here too. Good applications check permissions on the server for every request and restrict where the server may connect. See IDOR explained and SSRF explained.

A02Security Misconfiguration

Default passwords left unchanged, unnecessary features switched on, detailed error messages shown to visitors, or cloud storage left open. It moved up to second place in 2025 because so much of an application now depends on configuration. Careful, repeatable configuration and regular review help.

A03Software Supply Chain Failures

Applications are built from libraries, packages, build tools and pipelines written by other people. If one of them has a known flaw, is out of date or has been tampered with, the whole application inherits the risk. This category is new in 2025 and replaces the narrower "vulnerable and outdated components". Keep an inventory of what you use, update promptly and protect the build pipeline.

A04Cryptographic Failures

Sensitive data is not properly protected, for instance passwords stored in plain text, or data sent without encryption. The fix is strong, current encryption and careful key handling.

A05Injection

An attacker sends data that the application mistakenly treats as a command. SQL injection is the classic example: input typed into a login form changes the database query. Cross-site scripting is related, where the injected content is script that runs in another user's browser. Validating input and using parameterized queries prevents most of it. See SQL injection explained and XSS explained.

A06Insecure Design

The flaw is in the plan, not the code. A password reset that reveals whether an email exists, or a checkout with no limit on attempts, is badly designed however neatly it is coded. Threat modeling early catches these.

A07Authentication Failures

Weak login protections, such as allowing unlimited password guesses, accepting weak or leaked passwords, or mishandling sessions. Multi-factor authentication and sensible session handling reduce the risk.

A08Software or Data Integrity Failures

The application trusts code or data without verifying it, for example an update delivered without a signature check, or data from a user that it loads back as an object without checking. Verify the source of anything the application runs or loads.

A09Security Logging and Alerting Failures

If nothing is recorded, or nobody is alerted, attacks go unnoticed for months. Log important events, protect the logs and make sure alerts reach someone who acts on them. This is where web security meets the work of a SOC analyst.

A10Mishandling of Exceptional Conditions

New in 2025. Applications fail in unsafe ways when something unexpected happens: an error message that leaks internal details, a failed check that lets the request through anyway, or a crash under unusual input. Handle errors deliberately, and make the application fail closed, not open.

There Are Other OWASP Lists Too

Modern applications keep their data and rules in APIs, so OWASP publishes a separate API Security Top 10. Applications that include an AI assistant have their own list, the OWASP Top 10 for LLM Applications.