Existing protection was per-IP only (login_attempts table). On a loopback
deployment everyone hits 127.0.0.1, so the per-IP counter is mostly
ornamental — the real attacker is on the same machine. Adds a second
defense layer that tracks failures per username with an exponential
backoff schedule.
Schema:
account_lockouts (username TEXT PK, failed_count INT,
locked_until DATETIME, last_attempt_at, last_attempt_ip)
Backoff after threshold (4+ failures):
1, 2, 3 failures → no lockout (grace window for typos)
4th → 60 s
5th → 5 min
6th → 15 min
7th → 1 h
8th → 6 h
9th and beyond → 24 h (capped)
Counter resets to 0 on successful login or reauth. Old non-locked rows
older than 30 days are pruned by CleanupExpired alongside the existing
sessions / audit_log / login_attempts cleanups.
Wiring:
- HandleLogin / HandleReauth both check RejectIfAccountLocked() before
touching the users table. Lockout responses are 429 with JSON body
{ error, retry_after } and a Retry-After header.
- Failed attempts are recorded against the username even when the user
doesn't exist, preventing account enumeration via differential
"is this account locked?" probes.
- PBKDF2 hash comparison was already constant-time (ConstantTimeEquals);
no change there.
Client (js/app.js):
- api() now preserves response status + body on Error so callers can
distinguish 429-lockout from other errors.
- New showLockoutCountdown(seconds) renders a live "Account locked —
try again in Xm Ys" message in #authHint, disables #loginBtn until
the countdown reaches 0, then re-enables it.
- doLogin / doUnlock both branch on err.status === 429 + retry_after
to call showLockoutCountdown instead of a generic error toast.
Known limitation: an attacker can DoS-lock arbitrary usernames by
spamming /login with that name. This is intentional — the alternative
(per-(username,IP) tracking) would let attackers enumerate accounts.
DoS-lock is acceptable; auth bypass is not.
Zaki
9f6636defc