MCP Bastion

Security middleware for MCP. Blocks prompt injection, PII leakage, and resource exhaustion.

Quick Install

Automated & IDE Setup

Copy the AI prompt to install this server into Claude Code, Cursor, or another agent — or use 1-click editor setup below.

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Manual Client & Custom JSON ConfigExpand JSON ▾

Client Config & Setup

Choose your client or environment

Target File:~/Library/Application Support/Claude/claude_desktop_config.json

claude_desktop_config.json

{
  "mcpServers": {
    "mcp-bastion-2": {
      "command": "uvx",
      "args": [
        "mcp-bastion-python"
      ]
    }
  }
}

💡 Paste the JSON block into your client's configuration file under mcpServers, then restart the application.

Documentation Overview

MCP-Bastion

README · Documentation · Demos · Dashboard / Observability · Multi-language · Benchmark · License · Security

MCP-Bastion - Fortifying the Model Context Protocol

Current release: 5.1.0 · Docker v5.1.0 · 26 PyPI packages · CHANGELOG

Go to	Link
Docs / demos	https://vaquarkhan.github.io/MCP-Bastion/ · product tour video · integrations
Benchmark / security deck (PDF)	MCP-Security-Deck-v3.pdf · raw download
Documentation handbook	https://vaquarkhan.github.io/MCP-Bastion/guide/handbook.html
Demos (attacks, dashboard, payloads, all languages)	https://vaquarkhan.github.io/MCP-Bastion/guide/demos.html
Dashboard & observability (OTEL optional)	https://vaquarkhan.github.io/MCP-Bastion/guide/observability.html
Multi-language suite	https://vaquarkhan.github.io/MCP-Bastion/guide/multi-language.html · suite repo
MCP Test Harness (sister product — CI gate for MCP servers)	https://github.com/vaquarkhan/mcp-test-harness · use with Bastion E2E
Docs hub	https://vaquarkhan.github.io/MCP-Bastion/guide/
Measured benchmarks (reproducible)	docs/BENCHMARKS.md

The Zero-Trust control plane for MCP agents. Your agent can call databases, APIs, and shell tools. One bad prompt can leak PII; one runaway loop can burn your API budget in minutes; three agents on one server with no identity boundary is a confused-deputy incident waiting to happen. MCP-Bastion wraps your MCP server with local guardrails: agent IAM, supply-chain checksums, injection blocking, PII redaction, and denial-of-wallet caps, under 5ms overhead, with no third-party safety API.

Guiding rule: Stay a zero-infra, drop-in library - the guardrail brain that composes with any gateway, not a gateway itself. Strategy: docs/ZERO_INFRA_STRATEGY.md.

Measured proof (offline, reproducible)

Slide deck (share with evaluators): MCP-Security-Deck-v3.pdf — security + FinOps proof pack (direct download).

Gate	Result	How to reproduce
Injection heuristics	100% attack block · 0% benign FP on the published corpus	`pytest tests/test_injection_efficacy.py` · docs/BENCHMARKS.md
Tool catalog scan	Injection / secrets / homoglyphs / shadow tools / nested weak schemas	`mcp-bastion scan examples/fixtures/tools-poisoned.json`
FinOps	Up to ~99.7% output-budget savings · ~85% fewer discovery tokens	docs/BENCHMARKS.md
Toxic-flow taint	Session PII/secret → egress tool with URL/email args blocked in-process	`toxic_flow` in `bastion.yaml` · docs/THREAT_MODEL.md

MCP-Bastion: SCAN → TEST → ENFORCE - No other tool has all three

Scan → Test → Enforce (no other tool has all three)

Phase	What	Command
Scan	Static tool-definition checks before deploy (injection, secrets, homoglyphs, fingerprint drift, schema preconditions)	`mcp-bastion scan tools.json`
Audit	Local MCP client-config risk report (over-broad tools, standing credentials, filesystem servers)	`mcp-bastion audit`
Test	Integrated red-team against `bastion.yaml` + pair with MCP Test Harness in CI	`mcp-bastion redteam` · docs/BASTION_AND_TEST_HARNESS.md
Enforce	Runtime middleware on every MCP method	`secure_fastmcp(mcp)` or `bastion.yaml`

scan vs audit - different inputs, different questions

	`mcp-bastion scan`	`mcp-bastion audit`
Looks at	A tool catalog (`tools.json` / `tools/list` export)	MCP client configs on disk (`mcp.json`, Claude Desktop config, etc.)
Asks	“Is this tool metadata poisoned or drifted?”	“What can agents already reach on this machine?”
Finds	Injection in descriptions, secrets in schemas, homoglyphs, fingerprint drift, weak/unbounded inputSchema shapes	Over-broad tool grants (`*`), standing credentials in `env`, filesystem-server hints
When	Before you ship or attach a server’s tools (CI / pre-deploy)	Before you tighten policy on a laptop or workspace (local hygiene)

They complement each other: audit the host surface, then scan the tools you attach. Neither replaces runtime enforce.

mcp-bastion scan also accepts --skills DIR for offline agent skill-file checks. Dependency CVEs: mcp-bastion osv-refresh then mcp-bastion osv-scan (local DB default; --online opt-in, fail-open).

server.ts

# 1. Scan a tools/list export (or hand-authored catalog) - client-side, no cloud
mcp-bastion scan examples/fixtures/tools-poisoned.json
mcp-bastion fingerprint tools.json -o baseline.json
mcp-bastion scan tools.json --baseline baseline.json --format json -o report.json
mcp-bastion scan --skills ./skills/

# 1b. Audit local MCP client configs (what agents can already reach)
mcp-bastion audit --root .
mcp-bastion audit --format json -o risk-audit.json --fail-on none

# 2. Test policy effectiveness
mcp-bastion redteam --config bastion.yaml

# 3. Enforce at runtime (filesystem path guards when agents can read local files)
#    merge examples/bastion-filesystem-guards.yaml into bastion.yaml
mcp-bastion validate --config bastion.yaml

mcp-bastion scan CLI - flags injection, secrets, homoglyphs, and fingerprint drift with letter grade A–F

_{mcp-bastion scan - client-side static scanner; no cloud, no ML download}

Read the full README →View source on GitHub →

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Frequently Asked Questions about MCP Bastion

Add the following block to your claude_desktop_config.json under mcpServers: "mcpServers": { "mcp-bastion": { "command": "npx", "args": ["-y", "MCP-Bastion"] } }

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Technical Specs & Signals

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