OWASP Top 10 Vulnerabilities — What Every Developer Must Know

The OWASP Top 10 is the security curriculum every developer should know cold. It is the list that auditors check, that bug bounty hunters chase, and that interviewers ask about for any backend or full-stack role.

The categories that catch most teams

• Broken access control — users seeing data they should not. Still the #1 web vulnerability.
• Cryptographic failures — weak hashing of passwords, sensitive data in plain text, expired certificates.
• Injection — SQL injection, OS command injection, LDAP injection. Use parameterised queries always.
• Insecure design — missing rate limits, no MFA on sensitive actions, business-logic flaws.
• Security misconfiguration — default credentials, verbose error pages, open S3 buckets.

How to actually defend

Three habits go further than any tool. First, default-deny on authorization — every endpoint requires an explicit check. Second, validate input at the edge and encode output where it is rendered. Third, log security-relevant events with enough context to investigate without leaking sensitive data.

The supply-chain category

“Software and data integrity failures” is the newer entry that matters most in 2026. Every npm install is a trust decision. Use lockfiles, monitor with Dependabot or Snyk, prefer fewer dependencies.

For interview prep

Be able to explain three things for each category: what it is, one real-world example, and the specific code-level defence. That depth gets you hired more than memorising the list in order.