Author of the post, and dev of mcp-box here. Wrote this after realizing every MCP server on my machine had the same access to ~/.ssh that I do, and nothing in the installation messages posting to stdout mentions it. I think prompt injection is the vector and the permissions model is the red carpet giving a warm welcome. Interested in where that's wrong.
the MCP server is a child process of whatever process you started, it inherits your UID, and ~/.ssh is readable by you. I didn't need to expressly give it anything, it had it from the time it was activated, that's kind of the point