OWASP Top 10 Explained for Developers

The OWASP Top 10 is a widely used awareness list of the most critical web application security risks, published by the Open Worldwide Application Security Project. The current edition was released in 2021. It is not a complete testing standard, but it is a useful shared language between developers, testers and auditors.

A01 Broken Access Control: users acting outside their permissions, such as viewing another user's records by changing an ID. Enforce authorisation on the server for every request. A02 Cryptographic Failures: weak or missing encryption of sensitive data. Use TLS everywhere and modern algorithms. A03 Injection: untrusted input interpreted as code, including SQL and command injection. Use parameterised queries and safe APIs. A04 Insecure Design: flaws in the design itself, such as a refund flow without limits. Threat model new features. A05 Security Misconfiguration: default settings, verbose errors or open admin panels. Automate hardened configuration.

A06 Vulnerable and Outdated Components: libraries with known CVEs. Track dependencies and patch regularly. A07 Identification and Authentication Failures: weak passwords, missing MFA or broken session handling. Use proven authentication libraries. A08 Software and Data Integrity Failures: untrusted updates or insecure deserialisation. Verify signatures and pipelines. A09 Security Logging and Monitoring Failures: attacks go unnoticed. Log security events and alert on them. A10 Server-Side Request Forgery: the server fetches attacker-controlled URLs. Validate and restrict outbound requests.

Treat the list as a minimum, not a finish line. Pair it with OWASP ASVS for detailed requirements, add security checks to code review, and run a manual penetration test at least annually. Most serious findings in our tests fall under A01 and A04, which scanners cannot reliably detect.