Cybersecurity, learned like a practitioner.
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Most recent practitioner playbooks across every track. Filter by topic, level, or search in the sidebar.
Account Boundaries Are Negotiable
“Account boundaries protect us.” They do — until you create cross-account roles. Or federate identity. Or assume a role for a SaaS vendor. Each is a hole in the boundary. Each requires explicit authorisation. Most enterprises grant; few audit. The mindset: account boundary = sum of cross-account access. Inventory + audit quarterly.
Authentication vs Authorization Split
Authentication: who are you. Authorization: what can you do. Most security education conflates them. Most bugs live in the gap. An authenticated user is not authorized for everything they ask. Authorization is per-resource, per-action, often per-attribute. IDOR exists because authn is correct but authz is missing. The mindset: at every endpoint, two questions: “is this […]
Why Validation at Multiple Layers
Defence in depth is a phrase. Multi-layer validation is its application. Client-side validation catches user mistakes. Edge validation (WAF) catches bulk attacks. Server-side validation enforces business rules. Database constraints catch the rest. Each catches what the others miss. Skip a layer = bypass that layer’s coverage entirely. The mistake: assuming “the WAF catches it” or […]
State Machines Have More Edges Than You Think
Every web app is a state machine. Order = pending → paid → shipped → delivered. State transitions have rules. The rules have gaps. Attackers enumerate edges adversarially: can I go from pending to delivered, skipping paid? Can I cancel after shipped? Can I trigger paid → paid (double payment processing)? The mindset: draw the […]
The Three Types of Web Sessions
“Session” is overloaded: browser session (open tabs), server session (data keyed by session ID), application session (the user’s logical workflow). Each has different lifetime; each has different invalidation rules. The bug pattern: developer thinks “user logged out, session ended.” Browser session ended. Server session may persist. JWT may still be valid. OAuth refresh token still […]
Why HTTP Headers Are Programmable Trust
Application code routinely trusts HTTP headers. X-Forwarded-For for client IP. Host for routing. Origin for CORS. Each is attacker-controllable in some path. If your code does if (request.headers["X-Admin-Override"] == "true"), you’ve created a backdoor. If your code trusts X-Forwarded-For without validating the immediate peer, you’ve created an IP-spoofing primitive. The mindset: each header your code […]
CDN as Attack Surface
CDN was once a passive cache. Now: edge functions, header rewriting, cache key manipulation, custom routing. Each is a new attack surface. Cache poisoning, cache deception, edge-function privilege escalation, header injection between CDN and origin — all bug classes that didn’t exist when CDN was just static-asset cache. The mindset: list every CDN feature you […]
The 5 Trust Boundaries in Every Web App
Trust boundaries are where one component trusts data from another. Each crossing is a place to validate. Most apps have at least 5: Browser to server (the obvious one — input validation) Server to database (parameterised queries) Server to upstream API (output validation, response-content trust) Server to cache (cache-key collisions, deserialisation) Server to message queue […]
Reading Other People’s Code With Suspicion
Most code review looks for “does it work?” Security code review asks “does it work for inputs the author didn’t imagine?” The questions: What does the author assume about input format? What language quirk could surprise this code? What if this is concurrent? What if the dependency does something unexpected? What if the user’s session […]
Every Protocol Has Trust Assumptions
Every protocol — DHCP, ARP, DNS, BGP, NTP, IP, TCP — was designed for an environment with assumed cooperation. Attackers violate those assumptions. DHCP: trust whoever responds first. ARP: trust whoever claims an IP. DNS: trust whoever answers a query. BGP: trust whoever announces a route. Each assumption is a poisoning attack vector when the […]
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