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Brooks McMillin - Infrastructure Security Engineer

Infrastructure Security Engineer at Dropbox, focused on AI agent security, LLM development tooling, and securing production AI systems.

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Latest posts

A Coding Agent Read a File That Didn't Exist Five Times, Then Blamed the Tools

A Claude Code session confabulated a nonexistent Python file, persisted against five truthful "does not exist" errors, then self-diagnosed as corrupted tool output. A reconstruction from the raw transcript, a corpus scan across 3,001 sessions on whether the failure is worse in Opus 4.8, and a model-independent mitigation.

Wiring capability warrants into autonomous agents

Why OAuth scopes aren't enough for autonomous LLM agents calling MCP tools, and how we wired Tenuo capability warrants end-to-end. Scope-gated rollout, two real bugs, multi-hop delegation, and an attack the warrant catches.

Poisoning the Safety Net: Attacking AI Code Review Pipelines

Four months after writing about defense in depth for LLM-assisted development, I went back and tried to attack every layer of my own stack. The obvious attacks are caught by 2026 models. The class isn't closed; the cover stories got better.

mcp-authflow: OAuth 2.0 for Production MCP Servers

Open-sourcing mcp-authflow and mcp-authflow-resource: an RFC-compliant OAuth 2.0 framework for MCP servers, plus a one-command example server. Why MCP deployments need real auth, what the two packages do, and three non-obvious gotchas from production.

The MCP stdio Problem: Why I Rebuilt My Auth Proxy as a Persistent HTTP Service

Claude Code silently kills stdio MCP servers during idle periods, forcing manual reconnection. How I converted a fragile stdio bridge into a persistent Starlette HTTP reverse proxy — and the obscure SDK crash that followed.

Building Secure Agentic Systems: The Six Layers

Six layers of security architecture for running LLM agents as daily drivers — every design decision with production stats and companion code.

A Beginner's Guide to Safe LLM-Assisted Development

A complete beginner's guide to setting up every safety layer from the Coding Safer with LLMs post: pre-commit hooks, local review agents, CI workflows, and CLAUDE.md — starting from scratch.

Does Your System Prompt Actually Stop Prompt Injection? We Tested 10,000 Times to Find Out

An empirical study of 10,080 prompt injection attempts across 8 models, 6 defense strategies, and 7 attack types. The results challenge common assumptions about prompt-level defenses.

Defense in Depth for AI-Assisted Development: Pre-commit Hooks, Review Agents, and CI That Catch LLM Mistakes

Practical strategies for safer AI-assisted development: automated review agents, layered security checks, and context management that prevents catastrophic mistakes.

The Call is Coming from Inside the House: When your Agentic Coder Writes Dangerous Code

An introduction to the flaws in security testing for AI-generated code.