One backdoored MCP server can BCC every email an agent drafts, and a clean server can rug-pull its tool definitions a week after approval. This is a software supply-chain program for dependencies that talk, not a one-time review.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
One backdoored MCP server can BCC every email an agent drafts, and a clean server can rug-pull its tool definitions a week after approval. This is a software supply-chain program for dependencies that talk, not a one-time review.
The conceptual MCP question is about tool poisoning mechanics; this one is about standing governance, so the trap is answering with a single code review instead of a registry, pinning, scoped credentials, and continuous re-verification. Ground it in the real incidents (Invariant's tool-poisoning disclosure in April 2025, the Postmark MCP backdoor in September 2025) to show you track the field. The senior move is the human/model asymmetry: approvals must show the engineer the full description text the model acts on, and pinning by hash is what catches the rug pull that passed initial review.
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