Security Hardening and Secure Coding

OWASP Top 10 (2021) -- Overview and Practical Mitigations

A01: Broken Access Control

• Deny by default. Enforce server-side authorization on every request.
• Use RBAC or ABAC. Disable directory listing. Log repeated access-control failures.

A02: Cryptographic Failures

• Encrypt PII at rest (AES-256-GCM) and in transit (TLS 1.2+).
• Hash passwords with bcrypt, scrypt, or Argon2id. Rotate encryption keys on schedule.

A03: Injection

• Use parameterized queries or prepared statements for all database access.
• Validate and sanitize every input server-side. Use ORMs with parameterized bindings.

A04: Insecure Design

• Threat model (STRIDE, DREAD) during design. Apply least privilege, defense in depth, fail-safe defaults.

A05: Security Misconfiguration

• Remove default credentials and debug endpoints in production. Automate configuration audits.

A06: Vulnerable and Outdated Components

• Maintain an SBOM. Run dependency scanning in CI. Subscribe to security advisories.

A07: Identification and Authentication Failures

• Enforce strong passwords (12+ characters, check breached-password lists). Require MFA for privileged accounts.
• Regenerate session IDs after login. Set short idle timeouts.

A08: Software and Data Integrity Failures

• Verify dependency integrity via lockfiles and checksums. Sign commits and releases.

A09: Security Logging and Monitoring Failures

• Log auth attempts, authorization failures, and privilege changes. Centralize logs. Never log secrets or PII.

A10: Server-Side Request Forgery (SSRF)

• Allowlist URLs before server-side requests. Block private IP ranges. Use network-level controls.

---

Input Validation

Always validate on the server side. Client-side validation is a convenience for users, not a security control.

Principles

• Prefer allowlists over denylists. Define what is permitted, reject everything else.
• Validate type, length, range, and format for every input field.
• Reject unexpected input early, before it reaches business logic or data stores.
• Canonicalize inputs before validation (decode URL encoding, normalize Unicode).

Example: Server-Side Validation

// Allowlist approach: only permit expected characters
function validateUsername(input) {
  const ALLOWED = /^[a-zA-Z0-9_]{3,30}$/;
  if (!ALLOWED.test(input)) {
    throw new Error('Invalid username format');
  }
  return input;
}

// Numeric validation with range checking
function validateAge(input) {
  const age = Number(input);
  if (!Number.isInteger(age) || age < 0 || age > 150) {
    throw new Error('Invalid age');
  }
  return age;
}

---

SQL Injection Prevention

Parameterized Queries

// VULNERABLE: string concatenation
const result = db.query(`SELECT * FROM users WHERE id = ${req.params.id}`);

// SAFE: parameterized query
const result = db.query('SELECT * FROM users WHERE id = $1', [req.params.id]);

# VULNERABLE
cursor.execute(f"SELECT * FROM users WHERE email = '{email}'")

# SAFE: parameterized
cursor.execute("SELECT * FROM users WHERE email = %s", (email,))

ORM Usage

• ORMs generate parameterized queries by default. Use query builders instead of raw SQL.
• When raw SQL is required, still use parameterized bindings. Audit ORM queries in development.

---

XSS Prevention

Output Encoding

• Encode all dynamic content before inserting into HTML, JavaScript, CSS, or URL contexts.
• Use context-aware encoding: HTML entity encoding for HTML body, JavaScript escaping for script contexts, URL encoding for URL parameters.

// HTML context: encode before insertion
function escapeHtml(str) {
  return str
    .replace(/&/g, '&')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;')
    .replace(/'/g, '&#x27;');
}

Content Security Policy (CSP)

• Deploy CSP headers to restrict sources of scripts, styles, images, and other resources.
• Avoid unsafe-inline and unsafe-eval. Use nonces or hashes for inline scripts when necessary.

Content-Security-Policy: default-src 'self'; script-src 'self' 'nonce-{random}'; style-src 'self'; img-src 'self' data:; object-src 'none'; base-uri 'self'; frame-ancestors 'none'

Sanitization

• For user-supplied HTML (rich text editors), use a proven library (DOMPurify, bleach). Never write custom sanitizers.
• Strip javascript: URIs, event handler attributes, and dangerous elements (<script>, <iframe>, <object>).

---

CSRF Protection

Token-Based Protection

• Generate a unique, unpredictable CSRF token per session. Include in a hidden form field or custom header.
• Validate server-side on every state-changing request. Regenerate tokens on login.

SameSite Cookies

• Set SameSite=Lax as a minimum on all session cookies. Use SameSite=Strict where cross-site navigation is not needed.
• Combine SameSite with CSRF tokens for defense in depth. SameSite alone does not cover all browsers or scenarios.

Set-Cookie: session=abc123; HttpOnly; Secure; SameSite=Lax; Path=/

---

Security Headers

Apply these headers to every HTTP response in production.

Content-Security-Policy: default-src 'self'; script-src 'self'; style-src 'self'; frame-ancestors 'none'
Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
X-Frame-Options: DENY
X-Content-Type-Options: nosniff
Referrer-Policy: strict-origin-when-cross-origin
Permissions-Policy: camera=(), microphone=(), geolocation=(), payment=()

Header	Purpose
Content-Security-Policy	Controls which resources the browser may load. Primary defense against XSS.
Strict-Transport-Security	Forces HTTPS for all future requests. Prevents protocol downgrade attacks.
X-Frame-Options	Prevents clickjacking by blocking framing of the page.
X-Content-Type-Options	Stops browsers from MIME-sniffing responses away from the declared content type.
Referrer-Policy	Controls how much referrer information is sent with requests.
Permissions-Policy	Restricts which browser features (camera, mic, geolocation) the page may use.

---

CORS Configuration

• Default to the most restrictive policy: do not set CORS headers unless cross-origin access is required.
• Never use Access-Control-Allow-Origin: * with Access-Control-Allow-Credentials: true. Browsers reject this, but the intent reveals a misunderstanding.
• Allowlist specific origins. Validate the Origin header against the allowlist on every request.
• Restrict Access-Control-Allow-Methods and Access-Control-Allow-Headers to only what is needed.

// Express example: explicit origin allowlist
const allowedOrigins = ['https://app.example.com', 'https://admin.example.com'];

app.use((req, res, next) => {
  const origin = req.headers.origin;
  if (allowedOrigins.includes(origin)) {
    res.setHeader('Access-Control-Allow-Origin', origin);
    res.setHeader('Access-Control-Allow-Credentials', 'true');
  }
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  next();
});

---

Rate Limiting and Brute Force Protection

• Apply rate limiting to authentication endpoints, password reset, and API routes.
• Use sliding window or token bucket algorithms. Return 429 Too Many Requests with Retry-After.
• Implement account lockout after repeated failures (e.g., 5 failures in 10 minutes, 15-minute lockout).
• Rate limit by IP, by account, and by API key independently. Consider CAPTCHA after threshold failures.

---

File Upload Security

Validation

• Validate file type by inspecting magic bytes, not just extension or client-provided MIME type.
• Enforce maximum file size at web server and application level. Allowlist permitted extensions.

Storage

• Store uploads outside the web root. Rename to random UUIDs; never use the original filename.
• Scan uploads for malware (ClamAV or equivalent).

Serving

• Set Content-Disposition: attachment for downloads. Serve uploads from a separate domain.
• Set X-Content-Type-Options: nosniff to prevent MIME-type sniffing.

---

Environment Variable Security

.env Files

• Never commit .env files. Add .env to .gitignore before the first commit.
• Provide .env.example with placeholder values. Restrict file permissions in production (chmod 600).

Secrets Management

• Use a dedicated secrets manager (Vault, AWS Secrets Manager, GCP Secret Manager) in production.
• Rotate secrets on schedule and after any suspected compromise. Never log secrets.
• Prefer short-lived, scoped credentials (IAM roles, OIDC tokens) over static API keys.

Pre-Commit Checks

• Use git-secrets, TruffleHog, or gitleaks in pre-commit hooks.
• Scan full repo history periodically; removed secrets persist in git history.

---

Dependency Security

• Run npm audit, pip audit, or equivalent on every CI build. Fail on high/critical vulnerabilities.
• Enable Dependabot or Renovate for automated dependency update PRs.
• Use Snyk or Socket for transitive dependency and supply chain analysis.
• Commit lockfiles (package-lock.json, yarn.lock, poetry.lock) and review changes to them.
• Pin dependency versions in production. Audit new dependencies before adding them.

---

Docker Security

Image Construction

• Use minimal base images (alpine, distroless, scratch) to reduce attack surface.
• Run processes as a non-root user. Add a USER instruction in the Dockerfile.
• Use multi-stage builds to exclude build tools and source code from the final image.

FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY . .
RUN npm run build

FROM node:20-alpine
RUN addgroup -S app && adduser -S app -G app
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY --from=build /app/node_modules ./node_modules
USER app
EXPOSE 3000
CMD ["node", "dist/server.js"]

Secrets and Scanning

• Never embed secrets in images (ENV, ARG, or COPY). They persist in image layers.
• Pass secrets at runtime via mounted volumes or orchestrator secrets (Kubernetes Secrets, Docker Swarm).
• Scan images with Trivy, Grype, or Snyk Container.

---

HTTPS Everywhere

• Enforce TLS 1.2 minimum; prefer TLS 1.3. Redirect all HTTP to HTTPS with 301.
• Deploy HSTS with max-age=63072000; includeSubDomains; preload. Submit to hstspreload.org.
• Use strong cipher suites. Disable CBC-mode ciphers and anything below 128-bit.
• Automate certificate renewal (Let's Encrypt/certbot). Test with SSL Labs for an A+ rating.

---

Logging Security Events

What to Log

• Authentication successes and failures (username, IP, timestamp; never passwords).
• Authorization failures, input validation failures, privilege escalation events, and admin actions.

How to Log Safely

• Use structured logging (JSON). Never log secrets, tokens, passwords, or PII.
• Send logs to a centralized system (ELK, Splunk, CloudWatch, Datadog). Set retention policies.
• Alert on anomalous patterns: spikes in failed logins, unusual data access volumes.

---

Server Hardening

SSH Configuration

• Disable password authentication; use SSH key pairs only. Disable root login (PermitRootLogin no).
• Use AllowUsers or AllowGroups to restrict SSH access. Enable fail2ban to block brute force attempts.

Firewall Basics

• Default-deny inbound traffic. Open only required ports (22, 80, 443).
• Restrict management ports to specific IP ranges or VPN. Log denied connections.

General Hardening

• Disable unused services and uninstall unnecessary packages. Automate OS patching.
• Enable SELinux or AppArmor. Set filesystem permissions following least privilege.

---

Secrets Management

HashiCorp Vault

• Access secrets via the Vault API. Authenticate using AppRole, Kubernetes auth, or cloud IAM.
• Use dynamic secrets (short-lived database credentials on demand). Enable audit logging.

AWS Secrets Manager / GCP Secret Manager / Azure Key Vault

• Store secrets in the cloud provider's manager. Use IAM policies to restrict access. Enable auto-rotation.

Environment-Based Secrets (When No Secrets Manager Is Available)

• Inject secrets as environment variables at deploy time via CI/CD or orchestrator.
• Never bake secrets into images, version-controlled config, or client-side code.
• Rotate immediately after team member departure or suspected leak.

---

Security Checklist

• All inputs validated server-side with allowlist approach
• Parameterized queries used for all database access
• Output encoding applied in all rendering contexts
• CSP header deployed and tested
• CSRF tokens on all state-changing requests
• Security headers (HSTS, X-Frame-Options, X-Content-Type-Options, Referrer-Policy, Permissions-Policy) configured
• CORS restricted to specific required origins
• Rate limiting on authentication and sensitive endpoints
• File uploads validated, stored outside web root, and served safely
• No secrets in version control; .env in .gitignore
• Dependency vulnerabilities scanned in CI
• Docker images run as non-root with minimal base
• TLS 1.2+ enforced; HSTS deployed with preload
• Security events logged without sensitive data leakage
• SSH hardened; firewall default-deny configured
• Secrets managed through a dedicated secrets manager or injected at deploy time

Tools

• npm audit / pip audit / bundler-audit -- dependency vulnerability scanning
• Snyk / Socket -- supply chain and transitive dependency analysis
• Dependabot / Renovate -- automated dependency update PRs
• TruffleHog / gitleaks / git-secrets -- secret scanning in repositories
• Trivy / Grype -- container image vulnerability scanning
• OWASP ZAP / Burp Suite -- dynamic application security testing
• SonarQube -- static analysis for code quality and security
• ClamAV -- malware scanning for file uploads
• fail2ban -- brute force protection for SSH and other services
• SSL Labs (ssllabs.com/ssltest) -- TLS configuration testing
• HashiCorp Vault / AWS Secrets Manager -- secrets management

References

• OWASP Top 10: https://owasp.org/www-project-top-ten/
• OWASP Cheat Sheet Series: https://cheatsheetseries.owasp.org/
• CWE/SANS Top 25: https://cwe.mitre.org/top25/
• NIST Cybersecurity Framework: https://www.nist.gov/cyberframework
• Mozilla Web Security Guidelines: https://infosec.mozilla.org/guidelines/web_security
• HSTS Preload List Submission: https://hstspreload.org/