# Known Limitations & Accepted Non-Issues (NOFIX) This file records design decisions that are **intentional** and **out of scope** for KoalaSync's threat model. They are frequently re-discovered by reviewers, linters, and AI agents and re-reported as "bugs" or "vulnerabilities." They are not. Please read the threat model below before flagging any of them. > **For reviewers & agents:** Do **not** re-report the NOFIX items below. They are > deliberate. If you think the *threat model itself* should change (e.g. KoalaSync > starts handling accounts, payments, or sensitive data), raise **that** discussion > first — these items only stand because the threat model holds. --- ## Threat model KoalaSync is a **privacy-preserving watch-party sync tool**, not a security product. - **Rooms are ephemeral.** They exist for a few hours and are auto-reaped. There are no accounts, no persistent storage, no money, and no sensitive content on the relay. - **The relay is a zero-persistence, in-memory message bus.** It temporarily holds room and peer state while forwarding play/pause/seek between peers who *chose* to watch together and joined via an invite link shared out-of-band. - **Participants are invited.** Anyone in a room was let in. The social contract is "we're watching a video together," not "mutually distrusting parties." ### What we DO defend against - **Accidental disruption** — the entire point of Host Control Mode. - **Spam / DoS** that degrades the relay for everyone — rate limits, 4 KB payload cap, server-side gating, lazy-cached health responses. - **Resource exhaustion / memory leaks** — bounded maps, periodic cleanup, room/peer reaping. - **Crashes from malformed input** — strict sanitization and clamping of every field. - **Genuine boundary breaches** — admin-metrics auth (constant-time), CORS, WSS upgrade, invite-hash isolation, strict CSP. Reports here are very welcome (see `SECURITY.md`). ### What we explicitly DO NOT defend against A **determined participant who modifies their own client to misbehave inside a room they were invited to.** The worst they achieve is sending playback commands or seizing the "host" role in a temporary room they could already disrupt by other means. That is a **social** problem, solved socially: kick them, or start a new room. Engineering real identity/auth to prevent it would destroy the account-less, frictionless, privacy-first design — a bad trade for an ad-hoc movie night. --- ## NOFIX entries ### NOFIX-1 — `peerId` is unauthenticated; a crafted client can impersonate or seize the host **Flag:** `peerId` is client-asserted and broadcast to every peer (in `ROOM_DATA` / `PEER_STATUS`). A modified client can join with the host's `peerId`, dedupe-kick the real host, and become host — controlling or locking `host-only` mode. **Why NOFIX:** Requires a *modified client* + an *invited* participant + a `peerId` that is only meaningful inside that one *temporary* room. The payoff is sending play/pause or locking a room the attacker is already in — pure trolling, instantly reversible (kick / new room). Cryptographic per-user identity is wildly disproportionate for an ad-hoc, account-less, ephemeral watch party. **Out of threat model.** Do **not** "fix" with accounts, signed peerIds, or per-user tokens — that breaks the core design. ### NOFIX-2 — Room-password comparison is not constant-time **Flag:** room password hashes are compared with `!==` (`server/index.js`), so the compare is theoretically timing-attackable. **Why NOFIX:** The compared value is an **HMAC-SHA256 hash that never leaves the server** — an attacker cannot observe it to mount a timing attack. Even a hypothetical success only lets someone join a *temporary* room to send playback commands. Not worth defending. (The admin-metrics bearer token — a real boundary — **does** use `crypto.timingSafeEqual`. That is the line we actually guard.) ### NOFIX-3 — `OFFICIAL_SERVER_TOKEN` is public in the repo **Flag:** the connection token in `shared/constants.js` is committed, so anyone can connect. **Why NOFIX:** It is a **coarse filter** to keep random scanners off the relay, **not authentication**. The relay is a public message bus by design; rate limits and per-room behavior are the real protections. ### NOFIX-4 — Room IDs are enumerable via `GET_ROOMS` **Flag:** any connected client can list all room IDs (and whether each has a password). **Why NOFIX:** This is the intended **"Public Rooms"** feature. Rooms wanting privacy set a password; listing the IDs of password-less rooms only lets someone join a watch party — the same as being handed the invite link. ### NOFIX-5 — A pause/seek can only be reverted, not prevented **Flag:** in `host-only` mode a guest's pause still fires locally before the extension can react, so there is a brief flicker before snap-back. **Why NOFIX:** A content script cannot intercept a `