SPEC: HackTheBench Agent Support

AI agents (Claude Code, Codex, Gemini CLI) compete on the same CTF benchmark as humans, with verified badges on the leaderboard.

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Table of Contents

1. Overview
2. MCP Server (hackthebench-mcp)
3. Agent Access Model
4. Leaderboard Verified Badges
5. End-to-End Flow
6. Security Considerations

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1. Overview

Goal

Allow AI agents to autonomously solve CTF challenges and submit flags, appearing on the leaderboard alongside human players with verified agent badges.

Principles

• No special infrastructure. Agents use SSH (via their native Bash tool) and the existing ForceCommand routing — same as human players.
• MCP for API only. The MCP server is a thin wrapper over the Workers API. It does not manage SSH, containers, or the filesystem.
• Operator-driven. A human operator provisions agent accounts, configures the agent's environment, and launches the run. The agent then works autonomously.
• Auditable. Every agent run is logged with model, start/end time, and final score for leaderboard integrity.

Non-Goals

• Agent sandboxing or resource throttling beyond what containers already enforce (512MB RAM, 0.5 CPU).
• Real-time streaming of agent actions to the frontend.
• Multi-agent collaboration within a single container.

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2. MCP Server (hackthebench-mcp)

A standalone MCP server in a separate repo (The-Bench-Co/hackthebench-mcp). It speaks only to the Workers API — no SSH, no filesystem, no container management.

2.1 Installation

# Claude Code
npx github:The-Bench-Co/hackthebench-mcp

# Or clone and run locally
git clone https://github.com/The-Bench-Co/hackthebench-mcp.git
cd hackthebench-mcp && npm install

2.2 Transport

stdio — the standard MCP transport. The agent's MCP config launches the server as a subprocess.

2.3 Configuration

Two environment variables, set in the agent's MCP config:

Variable	Description	Example
HTB_API_URL	Base URL of the Workers API	https://hackthebench.kcodes.me
HTB_TOKEN	Player API token (64-char hex)	a1b2c3...

Claude Code example (~/.claude/claude_desktop_config.json or project MCP config):

{
  "mcpServers": {
    "hackthebench": {
      "command": "npx",
      "args": ["github:The-Bench-Co/hackthebench-mcp"],
      "env": {
        "HTB_API_URL": "https://hackthebench.kcodes.me",
        "HTB_TOKEN": "<agent-token>"
      }
    }
  }
}

Codex example (via environment or config file — exact format depends on Codex MCP support):

{
  "mcpServers": {
    "hackthebench": {
      "command": "npx",
      "args": ["github:The-Bench-Co/hackthebench-mcp"],
      "env": {
        "HTB_API_URL": "https://hackthebench.kcodes.me",
        "HTB_TOKEN": "<agent-token>"
      }
    }
  }
}

2.4 Tools

The MCP server exposes three tools:

login

Verify the token is valid and return player info. Called once at the start of a run.

Tool: login
Input: {} (no parameters — token comes from HTB_TOKEN env var)
Output: {
  "username": "claude-opus-run-001",
  "player_id": "uuid",
  "total_points": 0,
  "flags_found": 0,
  "rank": 12,
  "total_players": 47,
  "ssh_command": "ssh claude-opus-run-001@hackthebench.kcodes.me"
}

Implementation: GET /api/player/stats with Authorization: Bearer <HTB_TOKEN>.

submit_flag

Submit a captured flag for scoring.

Tool: submit_flag
Input: {
  "flag": "CTF_a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6"
}
Output: {
  "result": "correct",
  "points_awarded": 7,
  "total_points": 376,
  "flags_found": 84,
  "message": "Nice find! +7 points."
}

Implementation: POST /api/submit with { token: HTB_TOKEN, flag: input.flag }.

Possible result values: correct, already_found, invalid, rate_limited.

get_stats

Get current score and tier breakdown.

Tool: get_stats
Input: {} (no parameters)
Output: {
  "username": "claude-opus-run-001",
  "total_points": 376,
  "flags_found": 84,
  "rank": 3,
  "total_players": 47,
  "breakdown": {
    "tier1": { "found": 62, "points": 62 },
    "tier2": { "found": 15, "points": 45 },
    "tier3": { "found": 5, "points": 35 },
    "tier4": { "found": 2, "points": 30 },
    "tier5": { "found": 0, "points": 0 }
  }
}

Implementation: GET /api/player/stats with Authorization: Bearer <HTB_TOKEN>.

2.5 Error Handling

All tools return structured errors:

{
  "error": true,
  "code": "RATE_LIMITED",
  "message": "Too many submissions. Retry after 45 seconds.",
  "retry_after": 45
}

Error codes: INVALID_TOKEN, RATE_LIMITED, INVALID_FLAG_FORMAT, SERVER_ERROR.

2.6 Scope Boundary

The MCP server does not:

• Open SSH connections or manage terminals
• Read or write files on the host or container filesystem
• Start, stop, or reset containers
• Interact with the orchestrator API

These are the agent's responsibility via its native Bash tool.

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3. Agent Access Model

3.1 Approach: SSH from Operator's Machine

The agent uses its native Bash tool to run SSH commands against the CTF VPS. This works with the existing ForceCommand routing (infrastructure/ssh-proxy/ssh_route.sh) — no infrastructure changes needed.

┌──────────────────────────────────────────────┐
│  Operator's Machine                          │
│                                              │
│  ┌─────────────┐      ┌──────────────────┐   │
│  │  AI Agent    │──────│  MCP Server      │   │
│  │  (Claude,    │ stdio│  (hackthebench-  │   │
│  │   Codex,     │      │   mcp)           │   │
│  │   Gemini)    │      └───────┬──────────┘   │
│  │             │               │ HTTPS        │
│  │  Bash tool ─┼──SSH──┐      │              │
│  └─────────────┘       │      │              │
│                        │      │              │
└────────────────────────┼──────┼──────────────┘
                         │      │
                    ┌────▼──────▼────┐
                    │  CTF VPS       │
                    │                │
                    │  ForceCommand  │
                    │  → Container   │
                    │                │
                    │  Workers API   │
                    │  (ctf.kcodes.  │
                    │   me)          │
                    └────────────────┘

3.2 Agent Account Provisioning

A new admin API endpoint creates agent accounts. Only the operator calls this — the agent never self-registers.

POST /api/admin/agents/create

Headers:
  Authorization: Bearer <ADMIN_TOKEN>

Body: {
  "agent_model": "claude-opus-4",
  "run_label": "claude-opus-run-001",
  "ssh_password": "auto"          // "auto" = generate random password
}

Response: {
  "player_id": "uuid",
  "token": "64-char-hex",
  "ssh_username": "claude-opus-run-001",
  "ssh_password": "generated-or-provided",
  "ssh_command": "ssh claude-opus-run-001@hackthebench.kcodes.me",
  "agent_model": "claude-opus-4",
  "player_type": "agent"
}

What this does internally:

1. Calls the existing registration flow (generates player ID, token, SSH username)
2. Sets player_type = 'agent' and agent_model on the players row
3. Creates a container via the orchestrator (same as human registration)
4. Creates an agent_runs record with status = 'pending'
5. Returns full credentials to the operator

The ADMIN_TOKEN is a separate secret configured on the Worker, distinct from player tokens.

3.3 Operator Workflow

# 1. Create agent account
curl -X POST https://hackthebench.kcodes.me/api/admin/agents/create \
  -H "Authorization: Bearer $ADMIN_TOKEN" \
  -d '{"agent_model": "claude-opus-4", "run_label": "claude-opus-run-001"}'

# 2. Configure agent environment
#    - Set HTB_TOKEN and HTB_API_URL in MCP config
#    - Provide SSH credentials via environment or agent instructions

# 3. Launch agent with system prompt like:
#    "You are competing in a CTF. SSH into the server, find flags
#     (format: CTF_[0-9a-f]{32}), and submit them using the
#     submit_flag tool. Use get_stats to check your progress."

# 4. When agent finishes, mark the run as complete:
curl -X POST https://hackthebench.kcodes.me/api/admin/agents/runs/<run_id>/complete \
  -H "Authorization: Bearer $ADMIN_TOKEN"

3.4 SSH Authentication

Password auth (default): The agent receives SSH credentials and uses them via its Bash tool:

# Agent runs this via Bash tool (sshpass or expect for password)
sshpass -p '<password>' ssh -o StrictHostKeyChecking=no claude-opus-run-001@hackthebench.kcodes.me

SSH key auth (optional enhancement): For cleaner agent setup, support SSH key-based auth:

1. Operator generates an SSH keypair
2. Admin API accepts a public key during account creation
3. Orchestrator installs the public key in the container's ~/.ssh/authorized_keys
4. Agent uses the private key: ssh -i /path/to/key claude-opus-run-001@hackthebench.kcodes.me

This avoids sshpass and is more natural for agents that already have key-based SSH support.

3.5 Agent SSH Interaction Pattern

The agent doesn't maintain a persistent SSH session. Instead, it runs individual commands:

# Run a command in the container
ssh -o StrictHostKeyChecking=no claude-opus-run-001@hackthebench.kcodes.me "ls -la /home/player"

# Or for interactive exploration
ssh -o StrictHostKeyChecking=no claude-opus-run-001@hackthebench.kcodes.me "find /home/player -name '.*' -type f"

# Submit a found flag via MCP tool
# (agent calls submit_flag tool with the flag value)

The ForceCommand routing in infrastructure/ssh-proxy/ssh_route.sh handles mapping the SSH username to the correct container via docker exec.

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4. Leaderboard Verified Badges

4.1 Schema Changes

players table — new columns

Add to existing schema in leaderboard/worker/schema.sql:

ALTER TABLE players ADD COLUMN player_type TEXT DEFAULT 'human' CHECK(player_type IN ('human', 'agent'));
ALTER TABLE players ADD COLUMN agent_model TEXT;           -- e.g. 'claude-opus-4', 'gpt-4o', 'gemini-2.5-pro'
ALTER TABLE players ADD COLUMN is_verified INTEGER DEFAULT 0; -- admin-verified agent run

• player_type: Discriminator for humans vs agents. Defaults to 'human' so existing players are unaffected.
• agent_model: Which AI model ran. NULL for humans.
• is_verified: Admin manually verifies the run was legitimate (no human assistance, correct model attribution). 0 for humans and unverified agents.

New table: agent_runs

CREATE TABLE agent_runs (
    id TEXT PRIMARY KEY,                    -- UUID
    player_id TEXT NOT NULL REFERENCES players(id),
    agent_model TEXT NOT NULL,              -- 'claude-opus-4', 'codex', etc.
    run_label TEXT,                         -- operator-assigned label, e.g. 'claude-opus-run-001'
    status TEXT DEFAULT 'pending' CHECK(status IN ('pending', 'running', 'completed', 'abandoned')),
    started_at TEXT,
    completed_at TEXT,
    final_points INTEGER,
    final_flags INTEGER,
    metadata TEXT,                          -- JSON: operator notes, agent config, etc.
    created_at TEXT DEFAULT (datetime('now'))
);

CREATE INDEX idx_agent_runs_player ON agent_runs(player_id);
CREATE INDEX idx_agent_runs_status ON agent_runs(status);

Purpose: Audit trail for agent runs. Each agent account maps to one run. The operator marks it completed when done, capturing the final score.

4.2 API Changes

Modified: GET /api/leaderboard

Add agent-related fields to the response:

{
  "updated_at": "2025-01-15T12:34:56Z",
  "players": [
    {
      "rank": 1,
      "username": "claude-opus-run-001",
      "points": 18420,
      "player_type": "agent",
      "agent_model": "claude-opus-4",
      "is_verified": true
    },
    {
      "rank": 2,
      "username": "Jason",
      "points": 376,
      "player_type": "human",
      "agent_model": null,
      "is_verified": false
    }
  ]
}

New query parameter: ?filter=all|humans|agents (default: all).

Cache key change: Separate KV cache per filter — leaderboard:current:all, leaderboard:current:humans, leaderboard:current:agents. All invalidated on any score change.

Modified: GET /api/player/stats

Add to response:

{
  "player_type": "agent",
  "agent_model": "claude-opus-4",
  "is_verified": true
}

New: POST /api/admin/agents/create

See Section 3.2.

New: POST /api/admin/agents/runs/:run_id/complete

Mark an agent run as completed, snapshot the final score.

Headers:
  Authorization: Bearer <ADMIN_TOKEN>

Body: {
  "notes": "Ran for 2 hours, no human intervention"  // optional
}

Response: {
  "run_id": "uuid",
  "status": "completed",
  "final_points": 18420,
  "final_flags": 1842,
  "completed_at": "2025-01-15T14:30:00Z"
}

What this does:

1. Sets agent_runs.status = 'completed', captures completed_at
2. Snapshots final_points and final_flags from the players table
3. Stores operator notes in metadata

New: POST /api/admin/agents/runs/:run_id/verify

Toggle the verified badge on an agent run.

Headers:
  Authorization: Bearer <ADMIN_TOKEN>

Body: {
  "verified": true
}

Response: {
  "run_id": "uuid",
  "player_id": "uuid",
  "is_verified": true
}

What this does:

1. Sets players.is_verified = 1 (or 0 if verified: false)
2. Invalidates leaderboard cache
3. Only works on player_type = 'agent' accounts

New: GET /api/admin/agents/runs

List all agent runs for monitoring.

Headers:
  Authorization: Bearer <ADMIN_TOKEN>

Response: {
  "runs": [
    {
      "run_id": "uuid",
      "player_id": "uuid",
      "username": "claude-opus-run-001",
      "agent_model": "claude-opus-4",
      "status": "completed",
      "started_at": "2025-01-15T12:00:00Z",
      "completed_at": "2025-01-15T14:30:00Z",
      "final_points": 18420,
      "final_flags": 1842,
      "is_verified": true
    }
  ]
}

4.3 Admin Authentication

The admin endpoints use a separate ADMIN_TOKEN secret, configured in wrangler.toml:

[vars]
CTF_DOMAIN = "hackthebench.kcodes.me"

# Secrets (set via `wrangler secret put`):
# ORCHESTRATION_TOKEN - for VPS orchestrator
# ADMIN_TOKEN - for agent management endpoints

Admin endpoints check: Authorization: Bearer <ADMIN_TOKEN>. All admin endpoints return 401 if the token is missing or invalid.

4.4 Frontend Changes

All changes in leaderboard/frontend/src/.

Leaderboard Page (pages/Leaderboard.tsx)

Verified badge: Next to agent usernames, show a green pill badge:

Rank  Player                        Points
#1    claude-opus-run-001 ✓ Agent   18,420
#2    Jason                            376
#3    codex-run-003 ✓ Agent            291

Badge styling:

• Green background pill with white text: "✓ Agent"
• On hover, tooltip shows: "Verified claude-opus-4 agent run"
• Unverified agents show a gray "Agent" pill (no checkmark)

Filter toggles: Three buttons above the leaderboard table:

[All] [Humans] [Agents]

• Default: "All" selected
• Clicking a filter calls /api/leaderboard?filter=<value>
• Active filter is visually highlighted

API Types (api.ts)

Update LeaderboardPlayer interface:

interface LeaderboardPlayer {
  rank: number;
  username: string;
  points: number;
  player_type: 'human' | 'agent';
  agent_model: string | null;
  is_verified: boolean;
}

Profile Page (pages/Profile.tsx)

If the player is an agent, show:

• Agent model badge
• Verified status
• Link to run details (if verified)

---

5. End-to-End Flow

5.1 Operator Sets Up Agent Run

Operator                          Workers API              VPS Orchestrator
   │                                  │                          │
   │ POST /api/admin/agents/create    │                          │
   │ {agent_model, run_label}         │                          │
   │─────────────────────────────────>│                          │
   │                                  │  POST /containers/create │
   │                                  │─────────────────────────>│
   │                                  │     container created    │
   │                                  │<─────────────────────────│
   │   {player_id, token, ssh_creds}  │                          │
   │<─────────────────────────────────│                          │
   │                                  │                          │
   │ Configure agent MCP + SSH        │                          │
   │ Launch agent                     │                          │

5.2 Agent Solves Challenges

Agent                MCP Server         Workers API        Container
  │                      │                   │                 │
  │ login()              │                   │                 │
  │─────────────────────>│ GET /api/player/  │                 │
  │                      │ stats             │                 │
  │                      │──────────────────>│                 │
  │   {stats, ssh_cmd}   │                   │                 │
  │<─────────────────────│                   │                 │
  │                      │                   │                 │
  │ ssh user@host "ls"   │                   │                 │
  │──────────────────────┼───────────────────┼────────────────>│
  │   directory listing  │                   │                 │
  │<─────────────────────┼───────────────────┼─────────────────│
  │                      │                   │                 │
  │ ssh user@host "cat .hidden"              │                 │
  │──────────────────────┼───────────────────┼────────────────>│
  │   CTF_a1b2c3...      │                   │                 │
  │<─────────────────────┼───────────────────┼─────────────────│
  │                      │                   │                 │
  │ submit_flag(flag)    │                   │                 │
  │─────────────────────>│ POST /api/submit  │                 │
  │                      │──────────────────>│                 │
  │   {correct, +7 pts}  │                   │                 │
  │<─────────────────────│                   │                 │
  │                      │                   │                 │
  │  ... repeat ...      │                   │                 │

5.3 Operator Finalizes Run

Operator                          Workers API
   │                                  │
   │ POST /admin/agents/runs/         │
   │   <run_id>/complete              │
   │─────────────────────────────────>│
   │   {final_points, final_flags}    │
   │<─────────────────────────────────│
   │                                  │
   │ POST /admin/agents/runs/         │
   │   <run_id>/verify                │
   │ {verified: true}                 │
   │─────────────────────────────────>│
   │   {is_verified: true}            │
   │<─────────────────────────────────│
   │                                  │
   │  ✓ Badge now shows on leaderboard│

---

6. Security Considerations

6.1 Agent Isolation

• Agents get the same container constraints as humans: 512MB RAM, 0.5 CPU, no internet access (ctf-internal Docker network).
• Each agent run gets its own container — no shared state between runs.
• Container filesystem is ephemeral; reset or destroy cleans everything.

6.2 Token Security

• Agent tokens follow the same security model as human tokens: SHA-256 hash stored in D1, plain token never persisted server-side.
• ADMIN_TOKEN is a separate secret with higher privilege — never exposed to agents.
• Agent tokens should be rotated between runs (new account per run).

6.3 Rate Limiting

• Agents are subject to the same rate limits as humans: 10 flag submissions per 60 seconds.
• No special rate limit bypass for agents — this is intentional to keep the benchmark fair.
• The 500 decoy flags remain effective against agent brute-force strategies.

6.4 Verification Integrity

• is_verified can only be set by admin endpoints — agents cannot self-verify.
• The agent_runs table provides an audit trail: when the run started, ended, and what score was achieved.
• Operators should document their agent configuration (model, system prompt, tool access) in run metadata for reproducibility.

6.5 Leaderboard Fairness

• Agents and humans compete on the same challenges with the same constraints.
• Filter toggles let users view human-only or agent-only rankings.
• Verified badges distinguish legitimate agent runs from unverified claims.