mcp-bastion-fastmcp

Security middleware for FastMCP servers powered by MCP-Bastion.

Protect any FastMCP server from prompt injection, PII leakage, and resource exhaustion with a single import.

Install

pip install mcp-bastion-fastmcp

Usage

from mcp.server.fastmcp import FastMCP
from mcp_bastion_fastmcp import secure_fastmcp

mcp = FastMCP("My Secure Server")

# Add MCP-Bastion security to your server
secure_fastmcp(mcp)

@mcp.tool()
def get_weather(city: str) -> str:
    return f"Weather in {city}: 22C, sunny"

if __name__ == "__main__":
    mcp.run(transport="streamable-http")

What it protects

• Scans all tool arguments through the same MCPBastionMiddleware path as the core Python package (see defaults on the three toggles above)
• For full bastion.yaml features (semantic firewall, OPA/Cedar, allowlists, session limits, etc.), use build_middleware_from_config() with the low-level MCP Server - FastMCP does not expose a native hook for the entire policy surface

Implementation note: secure_fastmcp patches FastMCP._tool_manager.call_tool so every tool invocation flows through Bastion. Call it right after FastMCP(...) and before run().

License

Same terms as the MCP-Bastion project: see LICENSE. Non-commercial use is free with required citation/attribution; copyright terms apply. Commercial use as defined in the License may need a separate agreement (COMMERCIAL_LICENSE.md).