Unauthenticated MCP (Model Context Protocol) Server

Description

The application exposes a Model Context Protocol (MCP) server endpoint without requiring authentication. MCP is a standardized protocol that enables AI systems to discover and interact with external tools, data sources, and resources. Without proper authentication controls, any user or attacker can access this endpoint to enumerate all available tools and their capabilities, and potentially execute these tools to perform unauthorized operations. This represents a critical access control failure that exposes the application's internal functionality to unauthenticated parties.

Remediation

Implement comprehensive authentication and authorization controls for the MCP server to prevent unauthorized access:

1. Require Authentication for All MCP Endpoints
Implement token-based authentication using API keys, OAuth 2.0, or JWT tokens. Example implementation:

// Express.js middleware example
const authenticateMCP = async (req, res, next) => {
  const token = req.headers['authorization']?.replace('Bearer ', '');
  
  if (!token) {
    return res.status(401).json({ error: 'Authentication required' });
  }
  
  try {
    const user = await verifyToken(token);
    req.user = user;
    next();
  } catch (error) {
    return res.status(401).json({ error: 'Invalid or expired token' });
  }
};

app.use('/mcp', authenticateMCP);

2. Implement Role-Based Access Control (RBAC)
Restrict tool access based on user roles and permissions. Not all authenticated users should access all tools:

// Tool-level authorization example
const authorizeToolAccess = (toolName, userRole) => {
  const toolPermissions = {
    'database_query': ['admin', 'analyst'],
    'file_read': ['admin', 'developer'],
    'system_command': ['admin']
  };
  
  const allowedRoles = toolPermissions[toolName] || [];
  return allowedRoles.includes(userRole);
};

app.post('/mcp/tools/:toolName', authenticateMCP, (req, res) => {
  if (!authorizeToolAccess(req.params.toolName, req.user.role)) {
    return res.status(403).json({ error: 'Insufficient permissions' });
  }
  // Execute tool
});

3. Apply Rate Limiting
Prevent abuse by limiting the number of requests per user or IP address:

const rateLimit = require('express-rate-limit');

const mcpLimiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // Limit each user to 100 requests per window
  message: 'Too many requests, please try again later'
});

app.use('/mcp', mcpLimiter);

4. Enable Comprehensive Logging and Monitoring
Log all MCP access attempts, tool discoveries, and executions with user identification, timestamps, and outcomes. Set up alerts for suspicious patterns such as rapid enumeration attempts or repeated authorization failures.

5. Enforce TLS/SSL Encryption
Ensure all MCP communications occur over HTTPS to protect authentication tokens and sensitive data in transit.

6. Implement IP Whitelisting (Optional)
For internal tools, restrict MCP server access to trusted IP ranges or VPN connections.

7. Conduct Regular Security Audits
Periodically review exposed tools, their permission requirements, and access logs to identify and remediate potential security gaps.

References