The OWASP Top 10 was first published in 2003. It's been updated multiple times since. And the same fundamental vulnerability classes appear on every single edition because developers keep making the same mistakes, codebases keep inheriting the same patterns, and frameworks keep making the same insecure defaults easy to reach.

This isn't a knowledge problem. Most developers have heard of SQL injection and XSS. It's a practice problem - the gap between knowing a vulnerability exists and consistently writing code that prevents it. Here's that gap, closed.

1. SQL injection - still killing codebases in 2026

SQL injection should be a solved problem. Parameterized queries and prepared statements have existed for decades. And yet SQL injection remains in the OWASP Top 10 because developers still concatenate user input into SQL strings, usually when they're moving fast, copying old examples, or using raw query helpers in ORMs that technically exist but shouldn't be used.

The fix is non-negotiable: never concatenate user-supplied input into a SQL query. Always use parameterized queries or your ORM's safe query builder. If you must write raw SQL, use named parameters. Audit your codebase for string concatenation in database calls - grep for it, make your linter fail on it.

2. Broken authentication - the credentials problem

Broken authentication covers a family of related mistakes: storing passwords in plaintext or with weak hashing algorithms, failing to implement rate limiting on login endpoints, not invalidating sessions after password changes, and using predictable session token formats. Any one of these mistakes on a login system is a critical vulnerability.

In 2026: use bcrypt, scrypt, or Argon2 for password hashing - never MD5, SHA1, or unsalted SHA256. Implement exponential backoff on failed login attempts. Invalidate all sessions on password change. Use cryptographically random session tokens of at least 128 bits. Consider passkeys as a replacement for passwords entirely where possible.

3. Cross-site scripting (XSS) - the UI vulnerability with backend consequences

XSS happens when user-supplied content is rendered as HTML without proper escaping. An attacker injects a script tag that runs in victims' browsers, stealing session cookies, redirecting to phishing pages, or silently exfiltrating data. Modern JavaScript frameworks (React, Vue, Angular) escape content by default but every "dangerouslySetInnerHTML" call, every direct DOM manipulation, every server-rendered template that bypasses escaping is a potential XSS entry point.

Implement a strict Content Security Policy header. Audit every location in your codebase where raw HTML is rendered. Treat the framework's unsafe escape-bypass APIs as security-critical code requiring review.

4. Insecure direct object references (IDOR) - the access control gap

IDOR is embarrassingly simple: an API endpoint that takes an ID parameter and returns the corresponding resource, without checking whether the requesting user actually has permission to access that resource. Change /api/invoice/1042 to /api/invoice/1043 and you're reading someone else's invoice.

This is the most commonly found vulnerability in bug bounty programs because it requires no sophisticated tooling to discover, just curiosity. The fix: every request for a resource must verify that the authenticated user has authorization to access that specific resource. Every time. No exceptions.

5. Security misconfiguration - the deployment problem

Security misconfiguration is the highest-ranked category in OWASP Top 10 2021, and it encompasses a huge range of mistakes: default credentials left unchanged, debug endpoints exposed in production, verbose error messages that reveal stack traces and internal paths, S3 buckets left publicly readable, unnecessary services running and exposed, missing security headers.

The defense: treat your deployment configuration as code, review it with security eyes before every deployment, use automated configuration scanning tools (Scout Suite for AWS, Prowler for multi-cloud), and explicitly define expected headers and configurations in your deployment pipeline.

6–10: The remaining critical mistakes

Cryptographic failures: using outdated algorithms (MD5, SHA1, DES), hardcoding encryption keys in source code, storing sensitive data unencrypted, using HTTP instead of HTTPS for any user-facing traffic. Vulnerable and outdated components: dependencies with known CVEs that haven't been updated automate dependency scanning with Dependabot, Snyk, or socket.dev. Server-side request forgery (SSRF): accepting user-supplied URLs and making server-side requests to them, enabling attackers to reach internal services. Insecure deserialization: deserializing user-supplied data without validation, enabling object injection attacks. Insufficient logging and monitoring: not logging security events, not alerting on suspicious patterns, not having enough log detail to reconstruct an intrusion after the fact.

The one practice that catches most of these before production

Static application security testing (SAST) integrated into your CI/CD pipeline. Tools like Semgrep, SonarQube, and CodeQL run automatically on every pull request and flag security-relevant code patterns before they reach production. Combined with dependency scanning and a pre-production penetration test for significant releases, this layer catches the vast majority of the mistakes above before users are ever exposed to them. Security in code review is a practice, not a one-time audit.

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