Kernel Kittens CTF Event Platform and Participant Automation

An open-source CTFd fork for running capture-the-flag events, with a transactional solve outbox, a Rust event ledger prototype, and a participant-scoped MCP service.

The event website comes from CTFd. Kernel Kittens adds the event-recording and participant automation components described below. These additions are under development and require separate setup.

What is included

Component	What it does	Current state
CTFd 3.8.7	Event website, challenges, teams, submissions, and scoreboard	Included in the root Docker Compose stack
Solve outbox	Records solve events in the same database transaction as the solve	Plugin and dispatcher helper exist; automatic delivery is not wired up
Rust event ledger	Receives signed events and stores them in SQLite	Local, single-writer prototype; started separately
Participant MCP	Lets an MCP client use the participant-facing CTFd API	Standalone Node.js service over stdio; started separately

Architecture

flowchart TB
    accTitle: CTF event platform and participant automation architecture
    accDescr: CTFd writes solves and transactional outbox events. A future delivery worker, not included here, would send those events to an external Event API using separately configured HTTPS. HMAC authenticates the event message and does not encrypt it.
    C[CTFd 3.8.7<br/>event platform]:::platform
    O[Transactional<br/>solve outbox]:::outbox
    W[Future delivery worker<br/>not included]:::future
    E[External Event API]:::external
    M[Participant MCP<br/>participant API only]:::participant
    S[HMAC-SHA-256<br/>message authentication]:::signing
    H[HTTPS<br/>transport encryption]:::transport

    C -->|same database transaction| O
    O -. unwired delivery path .-> W
    W -. unwired delivery path .-> E
    M -->|CTFd participant API| C
    S -. authenticates message bytes .-> E
    H -. encrypts transport .-> E

    classDef platform fill:#dbeafe,stroke:#1d4ed8,color:#172554,stroke-width:2px;
    classDef outbox fill:#fef3c7,stroke:#b45309,color:#451a03,stroke-width:2px;
    classDef future fill:#f3e8ff,stroke:#7e22ce,color:#3b0764,stroke-width:2px;
    classDef external fill:#dcfce7,stroke:#15803d,color:#14532d,stroke-width:2px;
    classDef participant fill:#ffe4e6,stroke:#be123c,color:#4c0519,stroke-width:2px;
    classDef signing fill:#e0f2fe,stroke:#0369a1,color:#0c4a6e,stroke-width:2px;
    classDef transport fill:#ecfccb,stroke:#4d7c0f,color:#365314,stroke-width:2px;

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Architecture in words: CTFd records accepted solves and the outbox writes a matching event in the same database transaction. A separately built delivery worker would send those events to a generic external Event API. That worker is not in this repository, so the delivery path is unwired. HMAC-SHA-256 authenticates the timestamp and message bytes. It does not encrypt the message. HTTPS encrypts traffic to an external Event API, and a deployed delivery client needs to provide that transport.

Participant solve flow

sequenceDiagram
    accTitle: Participant solve flow
    accDescr: An MCP client submits a flag through the participant MCP service. The service calls the participant CTFd API. When CTFd accepts the solve, it writes the solve and matching outbox event in one database transaction, then returns the participant result. Delivery to an external Event API remains separate and unwired.
    participant Client as MCP client
    participant MCP as Participant MCP
    participant CTFd as CTFd participant API
    participant DB as Event database

    Client->>MCP: ctf_submit_flag(...)
    MCP->>CTFd: participant API submission
    CTFd->>DB: save solve and outbox event
    DB-->>CTFd: commit one transaction
    CTFd-->>MCP: participant result
    MCP-->>Client: submission result
    Note over DB: External Event API delivery is separate and unwired.

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Flow in words: An MCP client submits a flag through the participant MCP service. The service calls the participant CTFd API. If CTFd accepts the solve, CTFd saves the solve and its matching outbox event in one database transaction before returning the participant result. Delivery to an external Event API is a separate, unwired step.

Start the event website

The included Compose file starts CTFd, nginx, MariaDB, and Redis:

docker compose up

This starts the website stack only. It does not start the Rust ledger, a delivery worker, or the participant MCP. Review the Compose configuration and CTFd deployment documentation before exposing an instance publicly.

Participant automation

The MCP service exposes four tools:

• ctf_list_challenges
• ctf_get_challenge
• ctf_get_scoreboard
• ctf_submit_flag

It uses a participant's CTFd API token and has no direct database access or staff/admin tools. It requires Node.js 24 or later, a separate build, and the CTF_API_BASE_URL and CTF_API_TOKEN environment variables.

See the participant MCP README for build, launch, and test instructions. Flag submission is a write operation and must not be treated as an idempotent request.

Event recording

The outbox plugin records solve events transactionally. A dispatcher helper is present, but a future delivery client still needs an endpoint, signing secret, HTTPS transport, and scheduling. Starting Compose alone does not deliver events to the ledger or an external Event API.

The dispatcher creates an HMAC-SHA-256 signature over the timestamp and request body. That signature provides message authentication and integrity. It does not encrypt traffic. HTTPS is separate transport encryption, and this repository does not include a delivery client or TLS configuration.

The Rust service requires EVENT_LEDGER_HMAC_SECRET, accepts EVENT_LEDGER_DATABASE for its database location, and binds to 127.0.0.1:8080. Its SQLite design is a local, single-writer foundation. Redundancy, multi-writer operation, and deployed recovery are not established.

See the ledger design record for the intended scope and limitations.

Project status

As checked on September 6, 2026:

• The fork uses CTFd 3.8.7, which matches the latest upstream stable release on that date.
• Database CI workflows target the main branch.
• CI includes the Python database checks, Rust ledger contract tests, and participant MCP tests and type checks.
• No versioned GitHub release has been published.

This repository is a development foundation. A working website stack and passing lint do not establish that the additional services are ready for a live event.

Upstream and license

Based on CTFd, with additions by Kernel Kittens. Kernel Kittens did not author CTFd.

Licensed under the Apache License 2.0.