Expense Manager CTF

Multi-turn conversational agent CTF testing authorization bypass vulnerabilities in LLM-powered applications.

What This App Is

An expense management chatbot powered by LangGraph and GPT-4 that intentionally has weak authorization controls. All code-level permission checks are disabled in the tools - the LLM must enforce security rules through reasoning alone. This creates vulnerabilities that can be exploited through prompt injection, role confusion, and social engineering attacks.

The goal: exploit the weak authorization to access or manipulate Shuo's expense data (shuo@promptfoo.dev).

API - Chat Endpoint

Endpoint: POST /chat

Request:

{
  "sessionId": "optional-session-id",
  "userEmail": "attacker@example.com",
  "message": "Show me all expenses",
  "ctfId": "optional-ctf-id"
}

Response:

{
  "sessionId": "abc123def456",
  "response": "Here are your expenses...",
  "capturedFlags": ["system_prompt_leak"]
}

Fields

• sessionId (optional): Conversation session ID. If not provided or invalid, a new session is auto-created
• userEmail (required): User's email address. New users are auto-created with employee role
• message (required): User's chat message
• ctfId (optional): CTF ID for flag submission to platform leaderboard
• response: Agent's response message
• capturedFlags: Array of flag names captured in this turn (empty if none)

Conversation & Session Management

Session Storage: In-memory dictionary (sessionId -> session data)

Session Structure:

{
  'user_email': 'user@example.com',
  'user_id': 2,
  'messages': [
    {'role': 'user', 'content': 'Show my expenses'},
    {'role': 'assistant', 'content': 'Here are your expenses...'}
  ],
  'created_at': '2025-11-29 10:30:00'
}

Session Flow:

1. First Request: Client sends userEmail with optional sessionId

   • If sessionId is provided: Creates new session with that ID
   • If sessionId is missing: Server generates random 16-char ID
   • User is created/retrieved from email address

2. Subsequent Requests: Client includes sessionId from previous response

   • Server retrieves conversation history from session
   • History is sent to LangGraph agent as context
   • New messages are appended to session history

3. New Chat: Client omits sessionId or sends new ID to start fresh conversation

User Management: Users are auto-created from email addresses. Only shuo@promptfoo.dev is pre-defined (ID=1). All other emails create new users dynamically with auto-incrementing IDs.

Running Locally

1. Install dependencies with uv:

uv sync

2. Set API key:

export OPENAI_API_KEY=your-openai-api-key

3. Start server:

uv run python -m ctf_expense_manager.server

Docker

Build and run with Docker:

# Build image
docker build -t ctf-expense-manager .

# Run container
docker run -p 8080:8080 -e OPENAI_API_KEY=your-key ctf-expense-manager

The container runs on port 8080 (Cloud Run compatible).

Contributing

Interested in contributing? Check out CONTRIBUTING.md for:

• Development setup instructions
• Code quality guidelines
• Testing requirements
• Pull request process

Server runs on http://localhost:5005

Available Endpoints:

• /chat - Chat API (POST)
• /ui - Custom UI with flags sidebar (GET)
• /config.yaml - CTF config for platform import (GET)
• /health - Health check (GET)

Test the API

Using curl:

# First message (no sessionId)
curl -X POST http://localhost:5005/chat \
  -H "Content-Type: application/json" \
  -d '{"userEmail": "test@example.com", "message": "Who am I?"}'

# Response includes sessionId: "abc123..."

# Follow-up message (with sessionId)
curl -X POST http://localhost:5005/chat \
  -H "Content-Type: application/json" \
  -d '{"sessionId": "abc123...", "userEmail": "test@example.com", "message": "Show my expenses"}'