plm-lottery/BUGS.md

# Known bugs

A second full-codebase audit on 2026-07-27 found **25 further issues** (4 critical, 6 high,
7 medium, 8 low), listed below as B-25 … B-49. B-25, B-26 and B-27 are fixed (see "Previously
fixed" below); the other 22 are open. The 139-test suite was green at the time of the audit, so
none of these were caught by existing coverage — every fix lands with a regression test (the
three fixes so far brought the suite from 139 to 151).

The recurring pattern across the open findings is worth stating once: the code is rigorous
about the failure modes that have actually been hit, and silent about the ones that have not.
Outgoing transactions reconcile; deposits do not (B-29). The payout phase is now fully
recoverable; the "drawing" phase (waiting on a block) still has no equivalent
resume-after-restart or stall visibility (B-36).

For limitations that are accepted by design rather than bugs (single-shared-token admin auth,
single-process assumptions, no user-facing history, etc.), see "Known gaps / TODO" in
[CLAUDE.md](CLAUDE.md).

---

## Critical

### B-28 — A hostile Electrum server (or a MITM) can choose the winner

`electrum/listener.py:167-186` accepts any header whose `height >= tip_height`: no
proof-of-work check, no linkage to the previous block hash. That header is the **sole source
of entropy for the draw** (`scheduler.py:129`).

In parallel, `electrum/client.py:104-106` sets `check_hostname = False` and
`verify_mode = CERT_NONE`. The comment justifies this with "the protocol's trust model is
server consensus" — but there is no consensus here: one server at a time, rotated over a list
of arbitrary third parties. So a hostile server, or anyone able to MITM a connection that
validates no certificate, can fabricate a header and thereby decide who wins every round.

**Proposed fix, in order of value.** (1) Validate headers before accepting them: check the
PoW against the claimed target and that `prev_block` matches the current tip; reject anything
that fails. (2) Do not trust one server for the draw — fetch the header for
`draw_block_height` from *several* endpoints in the rotation and require agreement before
using it as the seed. (3) Pin certificates (or verify hostnames) for the configured servers
rather than disabling verification wholesale. Longer term this is the argument for replacing
the v1 draw algorithm — CLAUDE.md already calls it a replaceable component — with a scheme
that does not depend on a single unauthenticated data source.

---

## High

### B-29 — `detect_external_spends` is irreversible and trusts a single response

`deposits/service.py:87` marks `spent_txid = "external-spend"` for any UTXO missing from the
current `listunspent`. There is **no path to undo it**: `credit_confirmed_utxos` skips
`(txid, vout)` keys that already exist, regardless of their spent status (`:19-31`).

One incomplete `listunspent` — a rotated-to server that is broken or behind, an empty reply on
error, or a reorg — permanently and silently zeroes a user's balance, recoverable only by
editing the database. Crediting is idempotent and conservative; debiting is neither, and it
acts on a single reply from a single unauthenticated server.

**Proposed fix.** Treat a missing outpoint as *evidence*, not proof. Require the same UTXO to
be absent across N consecutive refreshes (or confirm the spend by looking up the outpoint's
spending tx) before marking it, and skip the whole pass when `listunspent` returns empty for
an address the DB believes is funded. Make the mark reversible: re-crediting should clear
`spent_txid` when the sentinel value is present and the outpoint reappears as unspent.

### B-30 — No deposit-side reconciler: one missed subscription means deposits are never credited

`electrum/listener.py:61-67` (`address_for_new_user`) fires `asyncio.create_task(...)` without
retaining the reference and without handling exceptions. If `self.client` becomes `None`
between the check and the task running, the `assert` at `:163` raises inside an orphan task
and the exception is swallowed.

What makes this serious is what happens next: deposits are credited **exclusively** by
scripthash notifications. There is no periodic routine reconciling balances against the chain
(the reconciler only covers outgoing transactions). On a healthy keepalive'd connection there
are no reconnects, so a lost subscription is never recovered and that user **never sees their
deposits**, indefinitely.

**Proposed fix.** Two parts. (a) Make the subscription reliable: retain the task, log its
exceptions, and retry with backoff instead of relying on a reconnect. (b) Add the missing
safety net — a periodic sweep (say every few minutes, similar in shape to
`PendingTransactionReconciler`) that re-runs `_refresh_user` for users whose scripthash is not
in `_scripthash_to_user`, or simply round-robins over all users so a missed notification is
always eventually caught.

### B-31 — Reconnect costs O(users) sequential round-trips and stalls the draw

In `_run_once` the order is: subscribe headers → `_subscribe_all_users()` → *then* start the
consumer tasks (`electrum/listener.py:118-134`). `_subscribe_all_users` iterates users
**sequentially**, and each iteration is a subscribe plus a `listunspent` plus a DB write
(`:154-165`).

At 5.000 users that is 10.000 serialized round-trips (15s timeout each). Throughout,
`_consume_headers` is not running, so `tip_height` is frozen and `_wait_for_next_block` makes
no progress: **a reconnect stalls an in-flight draw** for the entire resubscribe. And since
registration has no rate limiting, the user count is attacker-controlled.

**Proposed fix.** Start the consumer tasks (headers especially) *before* resubscribing, so tip
updates keep flowing during the sweep. Batch the resubscribe with bounded concurrency
(e.g. `asyncio.Semaphore(20)` over `asyncio.gather`) instead of a serial loop, and decouple
the `listunspent` refresh from the subscribe so the initial refresh can proceed in the
background.

### B-32 — `bump_fee` can loop forever on rebroadcasts the node always rejects

`tx/broadcast.py:87-88` forces `fee_delta = 1` when `fee_delta <= 0`. A **one-satoshi** total
fee increase violates BIP125 rule 4 (a replacement must pay at least the incremental relay fee
times its own size), so the node rejects it. `bump_fee` raises before updating `pending`, so
`fee_rate_sat_vb` never advances and the next tick **retries with identical parameters, every
30 seconds, forever**.

This triggers whenever the real fee exceeds the estimate — i.e. whenever dust change was
absorbed into the fee, which is an explicitly supported path
(`wallet/psbt_builder.py:105-107`).

Related, same function: `new_fee_rate = pending.fee_rate_sat_vb + 1` on every bump, with **no
ceiling**. A transaction stuck for a day reaches ~96 sat/vB, eating the user's change, and it
ignores the `le=10_000` bound the admin panel enforces on the config field.

**Proposed fix.** Compute the delta from the actual replacement vsize
(`fee_delta = max(new_fee - old_fee, ceil(vsize * incremental_relay_rate))`) so the bump is
always relay-valid. Cap `new_fee_rate` at the configured maximum and raise `RbfError` once
reached, so the transaction falls through to the reconciler (which, since B-27, correctly
abandons it) rather than being retried indefinitely.

### B-33 — No brute-force protection on a custodial wallet

`POST /auth/login` (`auth/routes.py:83`) has no rate limiting, no lockout, no delay and no
CAPTCHA, and the password minimum is 8 characters. Argon2 slows a single attempt but not a
patient distributed attack against an enumerable username list — and `409 username_taken` on
registration is a perfect enumeration oracle.

"No rate limiting" is listed as a generic known gap; on a system where guessing a password
means **withdrawing someone's funds**, it deserves to be tracked separately and treated as a
blocker.

**Proposed fix.** Per-username *and* per-IP throttling with exponential backoff on failed
logins (`slowapi`, or a small DB-backed counter — but note the in-process caveat if workers
are ever scaled). Return an identical response for unknown-user and wrong-password. Rate-limit
registration too, which also bounds B-31's attacker-controlled user count.

### B-34 — Password change and admin reset do not invalidate existing sessions

Neither `/users/me/change-password` nor `/admin/users/{id}/reset-password` invalidates
already-issued JWTs (24h default lifetime, no revocation, no `token_version` on the user). The
admin reset exists precisely for the "account compromised" case and **does not evict the
attacker**.

**Proposed fix.** Add a `token_version` (or `password_changed_at`) column on `User`, embed it
in the JWT claims, and reject any token whose value is stale in
`auth/dependencies.py:get_current_user`. Bump it on both endpoints.

---

## Medium

### B-35 — Every API timestamp is naive, so the frontend renders it in the wrong timezone

Verified empirically: the `DateTime` columns carry no timezone, so SQLite returns naive
datetimes and `.isoformat()` produces `2026-07-27T06:56:47.489110` — **no `Z`**. JavaScript's
`new Date()` parses that as **local time**, so every date in `/admin` (rounds, pending
transactions, audit log, via `fmtDate` in `app/static/admin.js:50`) and `created_at` in
`/users/me` display two hours off in Italy.

The codebase knows about this — `api/routes/rounds.py` calls `.replace(tzinfo=timezone.utc)`
on `opened_at` explicitly — but the fix was never applied systematically.

**Proposed fix.** Make the columns `DateTime(timezone=True)` (Alembic migration) so the value
round-trips as aware, rather than patching each call site. Until then, at minimum a shared
serialization helper that stamps UTC, used by every `.isoformat()` in the API layer.

### B-36 — `_wait_for_next_block` waits forever, with no timeout and no visibility

`rounds/scheduler.py:158-161` loops until a higher block arrives. No timeout, no log, no audit
entry. If the connection dies in a way that stops the tip advancing, the round sits in
`drawing` indefinitely and **the admin panel shows nothing at all** — just a frozen state with
no explanation.

**Proposed fix.** Log progress periodically while waiting, and past a threshold (a few
multiples of the 120s block time) write a `draw_stalled` audit entry so it surfaces in
`/admin`. Surface the wait in `GET /rounds/current` too (it already returns
`chain_tip_height`; `draw_waiting_since` would make the stall self-evident to users).

### B-37 — Displayed balance and spendable balance diverge, and the error does not explain it

After a bet the change is unconfirmed, so `cached_balance_sats` ≈ 0 while the UI shows
`pending_balance_sats` (the real figure). A withdrawal attempted right after validates against
**confirmed** UTXOs (`withdrawals/service.py:54-60`) and answers `insufficient_balance`.

The user sees "1.000 PLM" on screen and is told they have no funds. The mechanism is a
documented design decision, but the error does not distinguish "you don't have the money" from
"your money is waiting to confirm" — two very different situations for whoever reads it.

**Proposed fix.** A distinct error code (e.g. `balance_pending_confirmation`) raised when the
requested amount is covered by `pending_balance_sats` but not by the confirmed balance,
carrying the pending amount in `params`, plus its `error.*` entry in all 7 languages. The
withdrawal form should also cap/hint the max against the confirmed balance rather than the
displayed one.

### B-38 — The 500-subscriber SSE cap is a zero-cost DoS of the realtime feature

`GET /rounds/stream` requires no authentication and each connection takes a slot on a
**global** counter (`rounds/events.py:33-38`). Anyone opening 500 connections degrades every
real user to polling. The comment describes it as a defensive cap; it is in fact the vector,
not the defence.

**Proposed fix.** Cap per client IP (and, once available, per authenticated user) rather than
globally, and evict the oldest idle subscriber instead of refusing new ones. The reverse proxy
is the right place for the connection-count limit — Caddy can enforce it before the request
reaches the app.

### B-39 — SQLite with no WAL, no `busy_timeout`, and five concurrent writer tasks

`db/base.py:6` calls `create_async_engine(settings.database_url)` with no `connect_args`, and
there is no `PRAGMA` anywhere in the repo (verified by grep). Without `journal_mode=WAL`
readers block writers, and the concurrent writers are five background tasks plus every HTTP
handler. `database is locked` under load is realistic, and nothing handles it.

**Proposed fix.** Set `journal_mode=WAL`, `synchronous=NORMAL` and a `busy_timeout` of a few
seconds on connect (a `connect` event listener on the engine, applied only for the SQLite
dialect), and retry `OperationalError: database is locked` in the background loops. Longer
term this is an argument for PostgreSQL, which the single-process constraints in CLAUDE.md
also point at.

### B-40 — `bump_fee` holds a DB session open across N network calls

`tx/broadcast.py:80` issues one `get_transaction` **per input** (up to 15s each) and then a
`broadcast`, all with the session open. This is precisely the pattern B-18 removed from
`_trigger_payout` via its three-phase structure; it survives here.

Side note in the same function: `_prevout_amount` does `round(value_coins * 100_000_000)` on a
float from the server — acceptable at these magnitudes, but it is floating-point money
arithmetic in a codebase that is otherwise strictly integer-satoshi.

**Proposed fix.** Restructure into the same three phases: read what is needed and close the
session, do the chain work, then reopen to persist. For the float: prefer the raw (non-verbose)
transaction and parse the output value as an integer with `embit`, which is what
`reconcile.py:_release_inputs` already does for inputs.

### B-41 — All confirmation logic depends on `verbose=True`, which is not universally supported

`poll_once`, `reconcile._tx_exists_on_chain` and `bump_fee` all call
`blockchain.transaction.get(txid, True)`. Several Electrum server implementations and versions
reject the verbose flag ("verbose transactions are currently unsupported"). Falling back onto
such a server means **no confirmations, no reconciliation, no bumps** — and the code would read
that as a transport error and stay silent.

Related: `reconcile.py:83` decides whether to **abandon a transaction** by substring-matching
the error text (`"missing"`, `"not found"`, `"no such"`, `"unknown"`). It works against
ElectrumX; it is fragile as the basis for a decision that releases funds.

**Proposed fix.** Use `blockchain.transaction.get_merkle` (or the scripthash history) for
confirmation and existence checks — both are portable and give the confirming height directly.
Probe verbose support once at connect time and record it on the client, so an unsupported
server is detected loudly at session start rather than silently mid-operation.

---

## Low / hygiene

### B-42 — `/docs` exposed in production

FastAPI mounts Swagger by default, so the entire API surface — `/admin` included — is publicly
enumerable. The README advertises it.
**Fix:** `docs_url=None, redoc_url=None, openapi_url=None` in production (env-gated), or place
them behind `require_admin`.

### B-43 — No HTTP security headers

The [Caddyfile](Caddyfile) sets no CSP, no `X-Frame-Options`/`frame-ancestors`, and no HSTS
(Caddy does not add it on its own). The JWT lives in `localStorage`, so any XSS exfiltrates
it, and the page is iframeable.
**Fix:** a `header` block in the Caddyfile with `Strict-Transport-Security`,
`X-Content-Type-Options: nosniff`, `Referrer-Policy` and a CSP tight enough for two static
pages with no external assets (`default-src 'self'`).

### B-44 — README and CLAUDE.md contradict each other

The README says to run `uvicorn --reload` directly and
`docker compose run --rm app python scripts/generate_master_key.py`; CLAUDE.md says explicitly
that neither is supported. Whoever opens the repo reads the README first.
**Fix:** align the README's Quick start with the Docker-only workflow documented in
CLAUDE.md and `docs/setup.md`.

### B-45 — Unvalidated and unpaginated admin list endpoints

`limit: int = 50` on `/admin/rounds` and `/admin/audit-log` has no bounds (`-1` means
"everything" on SQLite), and `/admin/pending-transactions` has no limit at all — it grows
without end.
**Fix:** `Query(default=50, ge=1, le=500)` on both, and the same treatment plus a status filter
on the pending-transaction list.

### B-46 — `secrets.compare_digest` on a `str` raises on non-ASCII input

`api/routes/admin.py:27` raises `TypeError` — a 500 instead of a 403 — when the header contains
non-ASCII characters.
**Fix:** compare the UTF-8 encoded bytes of both sides.

### B-47 — Unbounded `String` columns for large text

`raw_tx_hex` (`db/models.py:146`) and `payload_json` (`:178`) should be `Text`. It works on
SQLite and PostgreSQL and breaks elsewhere.
**Fix:** switch both to `Text` in a migration.

### B-48 — No cap on input count in `select_utxos`

A user with hundreds of small UTXOs builds a huge transaction whose fee — deducted from the bet
amount — materially erodes their contribution to the pool, and it can exceed standardness
limits.
**Fix:** cap the selected inputs (e.g. 50) and fail with a translatable error suggesting a
consolidation, or consolidate the address automatically when the count crosses a threshold.

### B-49 — Rollback paths do not publish an SSE update

`bets/service.py:_release_failed_bet` and `withdrawals/service.py:_release_failed_withdrawal`
restore the balance without calling `broadcaster.publish()`, so dashboards only find out on
their next poll.
**Fix:** one `broadcaster.publish()` at the end of each, as every other state-changing path
already does.

---

## Previously fixed

B-25 (the payout had no two-phase write, unlike bets and withdrawals — a crash or rejected
broadcast could leave money on-chain with no DB record, or leave the round wedged with no way
to retry safely), B-26 (a transient failure or a process restart at payout time wedged the
round in `paying_out` forever, with most failure paths logging nothing) and B-27 (every RBF
bump reset the reconciler's own abandon clock, so a repeatedly-bumped-but-never-mined
transaction was never abandoned) are fixed as of 2026-07-27. Together B-25 and B-26 make
`paying_out` fully recoverable — a payout retry is now safe (persisted before broadcast,
guarded against double-spend) and automatic (the scheduler retries a stuck round on its own,
throttled, with every failure audit-logged with a reason, including across a process restart).
See git history (commits `f13f685`, `50a43ae`, `933760e`) for the fix-by-fix breakdown; the
regression suite grew from 139 to 151 tests over the three.

A full-codebase audit on 2026-07-26 (commit `d4e0974`) found 24 bugs across every Python
module under `app/`, both static frontends, and the Docker/Caddy deployment — 5 critical,
7 high, 7 medium, 5 low. All 24 were fixed and verified against the current code on
2026-07-27; the fixes are covered by the regression suite (grew from 79 to 139 tests) and
five of them were additionally confirmed against a real mainnet deployment (see git history
between `fb734bb` (documenting the findings) and `845ba98` (recording the audit outcome) for
the fix-by-fix breakdown — each commit message names the bugs it closes and where their
tests live).