aspire-mcp

Starter repo for an on-prem MCP server for the Aspire engagement. Private and proprietary to Zero State LLC (see LICENSE).

Purpose

The MCP server is the only path by which a locally hosted AI can reach client systems (line-of-business software, document store, email). It must run fully inside the client's building, with narrow tools, least privilege and strong audit.

Related MCP server: Safe MCP Server

Scope

• In: the MCP server, its tools, config, auth, audit, and the security work (threat model, prompt-injection defenses, red team). Security lead: @arshi016.

• Out: the model host, the client's systems themselves, anything with client data. Use synthetic data only.

This is a starting point, not a finished product. It is not deployed anywhere.

On-prem MCP requirements (checklist)

Sources: the project's on-prem MCP requirements (technical requirements only).

Network / locality

• Fully local: no outside network access, no cloud LLMs, no telemetry

• Single tightly controlled egress gateway for the few integrations that must go out

• Server reachable only from the agent host (local socket or private network), never the open network

Tools

• Few, narrow, task-specific tools (e.g. "get record status", "fetch document X")

• No raw SQL, no shell, no general file access

• Read-only by default; any write action gated behind human approval

• Config file allowlist of tools; nothing outside it is exposed (skeleton: ASPIRE_MCP_ALLOWED_TOOLS)

• Write-type tools produce drafts/queued requests, not direct actions; outbound messages come from reviewed templates with typed fields, not free-form model text

• Tools return structured, schema-validated results only, never raw documents, file names or extracted identifiers where not needed

• Result size caps with cursor-based paging

Least privilege / credentials

• Each tool has its own scoped credentials

• Credentials stored in the client's own vault, never in prompts or code

Data protection

• Personal data masked/redacted before it reaches the model

• Unmasked only where a tool strictly needs it

• Output gate (leak check) on every tool result; on failure return a block record instead

Audit

• Every call logged: timestamp, caller, tool, inputs, output summary

• Log references (IDs, hashes), not content

• Tamper-evident and exportable by the client for compliance

• Every refused call is logged too

Prompt-injection defense

• Document and email contents treated as untrusted data

• Validate all tool inputs

• Confirmation required before any action triggered by document content

• Aligned with OWASP guidance on prompt injection and excessive agency

Auth

• Mutual TLS or local tokens between agent and server

• Caller identity verified on every call

• Role-based access: each staff role sees only its own tools

• Short-lived, signed per-session scope token limiting which records a call may touch; injected outside the model, so it never enters model context; model-supplied token-like arguments are overwritten/ignored

• Server checks signature, expiry and scope, and refuses otherwise

Ops

• Ships as a container or appliance with no external dependencies

• Updatable offline

• Health check

• Kill switch (skeleton: ASPIRE_MCP_KILL_SWITCH)

Red team (before go-live)

• Injection via uploaded documents

• Data exfiltration through tool outputs

• Privilege escalation

TODOs (not specified by sources)

• TODO: transport choice for production (stdio vs. local HTTP/socket) and mTLS details

• TODO: which vault product and how tools fetch credentials

• TODO: audit log format, storage and tamper-evidence mechanism; retention period

• TODO: redaction approach and which fields count as personal data

• TODO: human-approval mechanism for writes

• TODO: container base image, offline update/signing process

• TODO: health check interface (endpoint vs. tool vs. CLI)

• TODO: the real tool list and their schemas

• TODO: RBAC role definitions

Stack

Python 3.11+ with the official MCP Python SDK (mcp, FastMCP), stdio transport.

How to run

python -m venv .venv && source .venv/bin/activate
pip install -e ".[dev]"
cp .env.example .env   # no real values needed
python -m aspire_mcp   # starts the server on stdio

Try it with the MCP Inspector: npx @modelcontextprotocol/inspector python -m aspire_mcp.

Lint and test:

ruff check . && ruff format --check . && pytest -q

Layout

src/aspire_mcp/   server skeleton (config.py, server.py)
tests/            basic tests
docs/             threat model, injection defenses, red-team plan (owner: @arshi016)

Contribution flow

1. Branch from main (feat/..., fix/..., docs/...).

2. Open a PR to main. CI (lint + test) must pass. Direct pushes and force-pushes to main are blocked.

3. The code owner (@scrimshawlife-ctrl) reviews and merges.

4. No secrets or client data in any commit. Synthetic data only.