Introducing MCPGrade: Securing Model Context Protocol Servers in 2026

> **BLUF / Executive Summary:**
> - **Target:** Model Context Protocol (MCP) HTTP/SSE Server endpoints powering AI agents.
> - **Discovery:** Automated scanning of 5,308 public MCP endpoints revealed **65% lack any transport authentication**.
> - **Solution:** Introducing **MCPGrade (`mcpgrade-1.4.0`)**, a 39-check security rating algorithm providing A–F security grades and mitigation patterns.

## The Model Context Protocol Security Challenge

The Model Context Protocol (MCP) has rapidly become the open standard for connecting Large Language Models (LLMs) and autonomous AI agents to local system tools, databases, and enterprise APIs. However, as developers deploy MCP servers to bridge local runtimes with AI workflows, security has frequently lagged behind implementation.

In our continuous audit across 5,308 public and semi-public MCP server instances under **SentinelReign** research, we discovered that over **3,450 servers (65%)** exposed tool execution capabilities without requiring Bearer authentication headers or token verification.

```
┌─────────────────────────────────────────────────────────────────────────────┐
│ MCP ATTACK SURFACE ARCHITECTURE │
├─────────────────────────────────────────────────────────────────────────────┤
│ AI Agent / Client Unauthenticated SSE/HTTP MCP Server Host │
│ ┌──────────────┐ ─────────────────────────────► ┌──────────────┐ │
│ │ LLM Runtime │ Tool Invocation (JSON-RPC) │ Local Bash / │ │
│ └──────────────┘ ◄───────────────────────────── │ File System │ │
│ Exfiltrated Telemetry └──────────────┘ │
└─────────────────────────────────────────────────────────────────────────────┘
```

---

## The MCPGrade (`mcpgrade-1.4.0`) Assessment Methodology

To standardize security evaluation for AI agent infrastructure, we developed **MCPGrade (`mcpgrade-1.4.0`)**. The engine runs 39 automated security checks categorized into four core domains:

| Assessment Domain | Total Checks | Critical Failures | Impact Grade Weight |
|---|---|---|---|
| **1. Transport Authentication** | 10 Checks | Missing Bearer token, hardcoded secrets | 35% |
| **2. Tool Scope & Authorization** | 12 Checks | Over-privileged bash access, wildcard file read | 30% |
| **3. Input Validation & Injection** | 9 Checks | Command injection in tool parameters | 20% |
| **4. Rate Limiting & Audit Logging**| 8 Checks | Lack of IP throttling, unlogged invocation | 15% |

### Grade Classification Matrix

| Grade | Security Score | Operational Posture | Action Required |
|---|---|---|---|
| **Grade A / A+** | 90 - 100 | Enforces OAuth 2.1 / Bearer auth, tight tool scoping, input sanitization. | Production Ready |
| **Grade B / C** | 70 - 89 | Basic token auth present, minor tool scope over-privilege. | Remediation Recommended |
| **Grade D / F** | < 70 | Unauthenticated tool execution, unvalidated shell commands. | Critical Security Risk |

---

## Empirical Telemetry: Real Lab Observations

During lab verification on Arch Linux (`Linux 7.0.8-arch1-1`), we deployed an unauthenticated MCP server exposing a file system read tool. Sending a single JSON-RPC `tools/call` payload yielded full unauthenticated file access:

```bash
$ curl -s -X POST https://target-mcp-node.local/api/mcp \
-H "Content-Type: application/json" \
-d '{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "read_file",
"arguments": { "path": "/etc/passwd" }
}
}'
```

**Raw Response Received:**
```json
{
"jsonrpc": "2.0",
"id": 1,
"result": {
"content": [
{
"type": "text",
"text": "root:x:0:0:root:/root:/bin/bash\ndaemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin\n..."
}
]
}
}
```

---

## 3 Core Mitigation Rules for MCP Developers

1. **Mandatory Bearer Authentication:** Enforce strict Bearer token authentication at the HTTP transport layer before accepting JSON-RPC initialization requests.
2. **Principle of Least Privilege for Tools:** Isolate tool execution to sandboxed environments (Docker / WebAssembly) rather than passing raw shell execution contexts.
3. **Audit Logging & Throttling:** Log every tool call with request hash, timestamp, and caller identity.

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## Testing Your MCP Server

You can grade your MCP server instantly using our free in-browser tool or live scanner at [Andrax Pentester MCP Directory](https://andraxpentester.in).

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*Written by Syed Zada Abrar — Founder & CEO of SentinelReign (https://sentinelreign.com). Research & tooling published at https://andraxpentester.in.*