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SecurityApr 15, 2026⏱ 8 min read
The 2026 Web Application Security Checklist Every Dev Should Follow
Web application security isn't glamorous, but the consequences of getting it wrong are severe. We've conducted security audits on 30+ applications over the past three years. The same vulnerabilities appear repeatedly — not because developers don't know about them, but because they're easy to overlook under deadline pressure. This checklist is designed to be actionable, not exhaustive.
Authentication & Session Management
- Enforce MFA for admin and high-privilege accounts
- Use secure, httpOnly, SameSite cookies for sessions
- Implement proper session invalidation on logout and password change
- Rate-limit login attempts and implement account lockout policies
- Never store passwords in plaintext — use bcrypt (cost factor ≥ 12) or Argon2
Input Validation & Injection Prevention
- Use parameterized queries / prepared statements — no dynamic SQL construction
- Validate and sanitize all user input server-side (client-side validation is UX, not security)
- Implement Content Security Policy (CSP) headers to mitigate XSS
- Use DOMPurify for any user-generated HTML rendered in the browser
// BAD: SQL injection vulnerability
$query = "SELECT * FROM users WHERE email = '" . $_POST['email'] . "'";
// GOOD: Parameterized query
$stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?");
$stmt->execute([$_POST['email']]);
API Security
- Authenticate every API endpoint — no unauthenticated access to business data
- Implement rate limiting per user and per IP on all public endpoints
- Return appropriate HTTP status codes (don't expose stack traces in 500 responses)
- Use HTTPS everywhere — never allow HTTP fallback in production
- Validate Content-Type headers on inbound requests
Data & Secrets Management
- Never commit secrets, API keys, or credentials to version control
- Use environment variables or a secrets manager (AWS Secrets Manager, HashiCorp Vault)
- Encrypt sensitive data at rest using AES-256
- Implement proper data retention and deletion policies (GDPR compliance)
Infrastructure & Deployment
- Keep all dependencies updated — run automated vulnerability scanning in CI (Snyk, Dependabot)
- Implement WAF (Web Application Firewall) rules for known attack patterns
- Use least-privilege IAM policies for all service accounts
- Enable audit logging for all authentication events and privileged actions
- Run SAST (static analysis) on every PR — don't wait for penetration tests
90% of the breaches we've analyzed exploited vulnerabilities that appear on the OWASP Top 10 list — a list that has existed since 2003. The basics, consistently applied, prevent most attacks.
💡 Start Here
If you do nothing else from this list, at minimum: use parameterized queries, hash passwords with bcrypt/Argon2, set security headers (CSP, HSTS, X-Frame-Options), and never commit secrets. These four things will prevent the majority of common attacks.
