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📘 PART V (j) — Fullstack Security for Seniors (Threat Modeling, OWASP-by-Pattern)

SECTION 0 — SECURITY IS A SYSTEM PROPERTY

Senior engineers don’t “add security.”

They design so insecure states are hard to reach.

SECTION 1 — THREAT MODELING (LIGHTWEIGHT, REPEATABLE)

For any feature, answer:

  • what are the assets? (accounts, money, data)

  • who are the attackers? (anon, user, insider)

  • what are the entry points? (API, UI, webhooks, uploads)

  • what’s the worst-case impact?

Output:

  • top 5 threats

  • mitigations

  • residual risk

SECTION 2 — OWASP BY PATTERN (WHAT SENIORS ACTUALLY APPLY)

XSS​

  • output encoding

  • avoid dangerouslySetInnerHTML

  • CSP

  • keep secrets out of JS (HttpOnly cookies)

CSRF​

  • SameSite cookies

  • CSRF tokens for unsafe methods

  • Origin/Referer checks

CORS​

  • explicit allow-list

  • never with credentials

SSRF​

  • avoid server-side fetch of user-provided URLs

  • egress allow-list + DNS/IP protections

Injection​

  • parameterized queries

  • validate inputs

Secrets / supply chain​

  • don’t commit secrets

  • dependency scanning

  • minimal permissions

SECTION 3 — SECURE-BY-DEFAULT API/UI PATTERNS

  • cookie vs token: prefer cookie (HttpOnly) for web refresh tokens

  • short-lived access tokens

  • least privilege scopes

  • audit logs for privileged actions

  • rate limits on auth + abuse endpoints

SECTION 4 — COMMON FLOWS: WHAT TO CHECK

  • Auth: session fixation, token replay, refresh storms

  • Uploads: validate magic bytes, scan before serving, signed URLs

  • Webhooks: signature verify, replay protect, idempotent handlers

  • Admin tools: strict authZ, strong auditing

SECTION 5 — EXERCISES

  1. Threat model your upload flow.

  2. Write CSRF defenses for your auth scheme.

  3. Define webhook verification + replay protection.

🏁 END — FULLSTACK SECURITY FOR SENIORS