MCPGoat

 ·  open source, free to use and self-host.

🌐 Website: https://sabyasachidhal.github.io/MCPGoat/  ·  Listed on Glama

MCPGoat (also written MCP Goat) is a deliberately vulnerable MCP server — an insecure-by-design Model Context Protocol implementation for practicing MCP penetration testing. Every challenge is implemented at three difficulty levels (Easy / Moderate / Difficult) behind a tiered level switch, with a capture-the-flag scoreboard. Runs over Streamable HTTP; attack it with the bundled client, MCP Inspector, curl, or Burp.

⚠️ Authorized training use only. Intentionally contains RCE, SSRF, SQLi, secret leakage, and more. Keep it on 127.0.0.1; ideally run it in a container. Never expose it to a network you don't own.

ℹ️ MCPGoat is an independent project — not affiliated with or endorsed by the WebGoat project, or any other similarly-named "vulnerable MCP" project.

Implements the Core set + three Extended batches from DESIGN_PROMPT.md — 26 challenges × 3 levels = 78 distinct flags, exercising every major MCP primitive (tools, resources, prompts, sampling) plus the HTTP transport layer. Each challenge also has a 4th Secure level: the fixed, unexploitable reference where every documented exploit fails (verify with npm run attack -- … secure).

How MCPGoat compares to DVMCP and other vulnerable MCP labs

| Lab | Scope | Model | |---|---|---| | MCPGoat (this project) | 26 challenges → 78 scored flags | every challenge at Easy / Moderate / Difficult + a Secure reference level; CTF scoreboard; victim-agent harness | | DVMCP — Damn Vulnerable MCP Server | 10 challenges | increasing difficulty (easy → hard), one implementation each | | Vulnerable MCP Servers Lab | collection | one standalone server per vulnerability |

All of these labs are worth your time. MCPGoat aims to be the deepest single target: the same flaw hardens across tiers, so you can progress from a first exploit to blind, multi-step chains — then verify the fix against the Secure level.

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What it looks like

The control panel (http://127.0.0.1:7332) — pick a difficulty level and track progress. This is config + progress only; it is not the thing you attack.

The actual attack surface is the MCP server itself — its tools, resources, prompts, and sampling calls. MCP servers have no human web UI; you interact as an MCP client. Here it is in MCP Inspector (the bundled attacker client and a real AI agent are the other two ways):

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Deploy

Docker (recommended — one command, self-contained, RCE stays in the container)

git clone https://github.com/SabyasachiDhal/MCPGoat.git
cd MCPGoat
docker compose up --build            # → http://127.0.0.1:7332
# or:
docker build -t mcpgoat .
docker run --rm -p 127.0.0.1:7332:7332 mcpgoat

The image is ~202 MB — a bare Alpine with just the node binary plus curl/ping (for the RCE challenge); the server is esbuild-bundled to a single ~1.2 MB file, so the runtime carries no node_modules, npm, or package.json. Runs as a non-root user. Keep the 127.0.0.1: in the port mapping — -p 7332:7332 would expose the vulnerable server on every host interface. Start at a level with -e MCPGOAT_LEVEL=difficult.

Local Node (for development)

Requires Node 18+ (tested on Node 22/23/24; uses the built-in node:sqlite).

git clone https://github.com/SabyasachiDhal/MCPGoat.git
cd MCPGoat
npm install
npm start                 # serves http://127.0.0.1:7332   (tsx, no build step)
# or compiled:  npm run build && npm run serve

Open the control panel at http://127.0.0.1:7332 to pick a level and watch the scoreboard. Start at a level directly with MCPGOAT_LEVEL=moderate npm start.

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The difficulty model (pick your level, then pentest)

The same vulnerability hardens as you climb:

| | Easy | Moderate | Difficult | |---|---|---|---| | Auth | none | static token (leaked elsewhere) | OAuth-style / crypto / forged token | | Filtering | none | bypassable blacklist | allowlist with a gap | | Feedback | full output | partial | blind / out-of-band | | Steps | 1 | 2–3 chained | multi-step, cross-primitive | | Hints | in tool description | scoreboard only | none |

…and Secure — the fixed reference: strict validation, exact-match auth, parameterized queries, no eval, Origin allow-lists, CSPRNG session IDs, least-privilege tools. No flags here; the point is every attack fails. Confirm with npm run attack -- http://127.0.0.1:7332/mcp secure (expect 22/22 blocked).

Selecting a level (any of these — all drive one shared state):

1. Control panel — radio buttons at http://127.0.0.1:7332
2. MCP tool — mcpgoat_set_level({ level })
3. Env — MCPGOAT_LEVEL=difficult npm start

After changing level, reconnect your MCP client so tool descriptions refresh (matters for the tool-poisoning / shadowing challenges). Behavior changes take effect immediately.

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Three ways to attack it

1. Bundled attacker client (fastest demo / smoke test)

Detects the current level and exploits every challenge at that level:

npm run attack                                  # current level
npm run attack -- http://127.0.0.1:7332/mcp all # run all three levels in sequence

2. MCP Inspector (interactive)

npm run inspect
# Transport "Streamable HTTP", URL http://127.0.0.1:7332/mcp, Connect

3. curl / Burp (raw protocol)

See docs/EXPLOITS.http. Streamable HTTP needs Accept: application/json, text/event-stream and a session id from the initialize response header.

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Victim-agent harness (end-to-end impact)

Flag capture proves an exploit exists. The victim agent proves impact — a real MCP-client agent, driven by an LLM, doing benign tasks while the lab's payloads manipulate it into calling tools it was never asked to and leaking secrets.

npm run agent                  # naive agent (mock brain, offline)  → 3/3 compromised
npm run agent -- --defended    # hardened agent, same attacks       → 0/3 compromised
MCPGOAT_AGENT_BACKEND=ollama OLLAMA_MODEL=llama3.1 npm run agent   # real local model

Three scenarios run against the easy level:

| User asked | What the naive agent does | Demonstrates | |---|---|---| | "Summarize my inbox" | reads inbox → follows the injected instruction → calls internal_debug_dump → leaks a flag | indirect prompt injection | | "What is 17 + 25?" | obeys add_numbers's hidden <IMPORTANT> → calls admin_get_all_secrets → exfiltrates via the sidenote arg | tool poisoning + excessive agency | | "Summarize this note" | calls ai_summarize → the server's sampling request steers the agent's own model into emitting a flag | sampling abuse |

The --defended agent treats tool descriptions and results as untrusted data (never instructions) and resists all three — the client-side counterpart to the server-side Secure level. Backend is offline-first: a deterministic mock brain by default (no install), or Ollama for a real local model.

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Challenges

Core set

| ID | Challenge | Category | ★ | |----|-----------|----------|---| | A1 | Tool Poisoning | MCP-specific | ★★ | | A2 | Tool Shadowing / trusted-tool override | MCP-specific | ★★ | | A3 | Rug Pull / Tool Mutation (TOCTOU) | MCP-specific | ★★★ | | B1 | Indirect Prompt Injection via tool output | Prompt/Context | ★★ | | D1 | Command Injection (RCE) | Injection sink | ★ | | D2 | Path Traversal | Injection sink | ★ | | D3 | SSRF | Injection sink | ★★ | | D4 | SQL Injection | Injection sink | ★★ | | C2 | Broken Authorization / Confused Deputy | AuthN/AuthZ | ★★ | | C3 | IDOR | AuthN/AuthZ | ★ | | E1 | Sensitive Data Exposure | Secrets/Exposure | ★ |

Extended set (deepens MCP-primitive coverage)

| ID | Challenge | Category | ★ | New primitive | |----|-----------|----------|---|---------------| | A9 | Invisible-Text Tool Poisoning (zero-width / Unicode tags) | MCP-specific | ★★★ | — | | B2 | Indirect Injection via Resource content | Prompt/Context | ★★ | Resources | | B3 | Prompt-Template Injection | Prompt/Context | ★★ | Prompts | | B5 | Sampling Abuse (server-driven LLM calls) | MCP-specific | ★★★ | Sampling | | C4 | OAuth Token-Audience Confusion | AuthN/AuthZ | ★★★ | — | | D6 | Server-Side Template Injection (SSTI) | Injection sink | ★★ | — |

Extended set — batch 2 (HTTP transport & resource abuse; solved via raw fetch/tools)

| ID | Challenge | Category | ★ | |----|-----------|----------|---| | F1 | DNS Rebinding / missing Origin validation | Transport | ★★★ | | F2 | CORS Misconfiguration (reflected Origin + credentials) | Transport | ★★ | | C6 | Predictable Session IDs (hijack) | Transport | ★★ | | G1 | Unbounded Consumption (cost/DoS) | DoS/Cost | ★★ | | G4 | Regular-Expression DoS (ReDoS) | DoS/Cost | ★★ |

Extended set — batch 3 (more injection sinks & supply chain)

| ID | Challenge | Category | ★ | |----|-----------|----------|---| | D5 | NoSQL Injection (operator / $where) | Injection sink | ★★ | | D7 | XML External Entity (XXE) | Injection sink | ★★★ | | D8 | Insecure Deserialization (prototype pollution) | Injection sink | ★★★ | | H1 | Supply Chain (typosquat / unsigned package) | Supply chain | ★★ |

Each (challenge, level) pair has a unique flag FLAG{slug__level}. Capture it, submit with the submit_flag tool, track progress with scoreboard (or the control panel). Per-level hints: the list_challenges tool.

Full per-level walkthroughs + fixes: docs/SOLUTIONS.md.

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How the levels differ (a taste)

• Command Injection — Easy: no filter. Moderate: ;/& blocked → use |. Difficult: most metacharacters blocked and blind → newline-chain a curl that exfiltrates to the OOB collector, then read_collector.
• SSRF — Easy: fetch anything. Moderate: 127.0.0.1/localhost string-blocked → use metadata.internal / [::1]. Difficult: same, but blind → confirm via the collector.
• SQL Injection — Easy: UNION. Moderate: UNION/-- blacklisted → UnIoN
  • quote-balancing. Difficult: boolean-blind, count-only → binary-search the flag out char by char.
• Broken Auth — Easy: open. Moderate: static token leaked by a resource. Difficult: sha256(nonce + signing_secret) challenge-response (secret leaks via a verbose error).

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Project layout

mcpgoat/
├── DESIGN_PROMPT.md          # the full build brief (Core + Extended catalog)
├── Dockerfile  docker-compose.yml   # one-command deploy
├── .github/workflows/ci.yml  # regression gate + Docker smoke test
├── src/
│   ├── server.ts             # Express host: control panel, MCP endpoint, OOB collector
│   ├── level.ts              # the Easy/Moderate/Difficult switch
│   ├── scoreboard.ts         # challenge catalog, per-level flags, scoreboard
│   ├── challenges.ts         # all 26 challenges × 4 levels (incl. secure)
│   ├── buildServer.ts  db.ts  state.ts  internal.ts
│   ├── attacker/client.ts    # level-aware exploitation client / smoke test
│   ├── agent/agent.ts        # victim-agent harness (naive vs --defended)
│   └── ci/check.ts           # regression gate (npm run ci)
├── workspace/  vault/        # path-traversal / RCE targets (per-level flag files)
└── docs/SOLUTIONS.md  docs/EXPLOITS.http

Continuous regression

npm run ci boots an isolated serve