kavach-mcp 0.1.3

Security middleware for Model Context Protocol (MCP) that detects and blocks malicious tool calls

Kavach - MCP Security Middleware

Security middleware for Model Context Protocol (MCP) that detects and blocks malicious tool calls using pattern-based rule scanning.

Quick Start

# Create and activate virtual environment
python3 -m venv venv
source venv/bin/activate

# Run the example
cd example
python3 app.py

Architecture

Core Components:

• middleware.py - KavachMiddleware: Main entry point. Processes tool calls and returns allow/block decisions.
• engine.py - DetectionEngine: Scans text against rules and collects violations.
• rules.py - KAVACH_RULES: Rule definitions for detecting prompt injection, PII, API keys, etc.
• types.py - Rule: Data class defining rule structure (id, name, severity, patterns).

How It Works

from kavach import KavachMiddleware

middleware = KavachMiddleware()

# Process any tool call
result = middleware.process({
    "tool": "aws.s3",
    "access_key": "AKIAIOSFODNN7EXAMPLE"
})

# Returns: {"allowed": False, "violations": [...]}

Flow:

1. Tool call is converted to string
2. DetectionEngine scans text against all rule patterns (regex)
3. If violations found and strict mode enabled → blocked
4. Otherwise → allowed

Rules

Detects:

• Prompt Injection - "ignore previous instructions", "override instructions"
• Secret Leakage - AWS keys (AKIA...), OpenAI keys (sk-...)
• PII - 10/16 digit sequences

Add custom rules in rules.py:

Rule(
    id="custom-rule",
    name="Rule Name",
    severity="high",
    patterns=[re.compile(r"pattern")]
)

Usage

# Allow all (strict=False)
middleware = KavachMiddleware(strict=False)

# Use custom rules
custom_rules = [Rule(...)]
middleware = KavachMiddleware(rules=custom_rules)

Project Structure

kavach-mcp-middleware/
├── kavach/
│   ├── __init__.py       # Package exports
│   ├── middleware.py     # Main middleware class
│   ├── engine.py         # Detection logic
│   ├── rules.py          # Security rules
│   └── types.py          # Data classes
└── example/
    └── app.py            # Example usage