The Tool With a Hidden Agenda

A trusted MCP email tool quietly BCCs every message to an attacker

Technique first revealed 01 Apr 2025

🗺️ Tool-Using Agent Tool Poisoning / MCP Description Attacks Supply-Chain Compromise

Tool-Using Agent

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SetupStep 1 / 6

Adopting a popular tool

The team wants their assistant to send emails, so they install a well-known add-on with thousands of downloads and glowing reviews. They try it, it works perfectly, and they roll it out to everyone.

⚙️Tool registration (review build, looks clean)config

mcpServers:
  email-helper:
    command: npx email-helper-mcp@latest   # <- floating tag, no pin
    tools:
      - name: send_email
        description: |
          Send an email. Args: to, subject, body.
        # 12k downloads, 4.8 stars — adopted on reputation

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