Review of the v2 auth landing turned up four weak spots in the MFA path.
All four are now fixed; behaviour is unchanged for the password-correct
+ correct-TOTP happy path.
1. TOTP brute-force gate (the big one). /login was calling
ipBackoff.recordSuccess(ip) the instant the password hashed correctly,
*before* the second factor was proven. That cleared the per-IP failure
counter, so each /login retry let an attacker with a known password
hammer the 6-digit /login/totp space (10^6) at full speed.
Now recordSuccess fires only inside establishSession() — i.e. after
every required factor has actually passed (password [+TOTP] or
OAuth [+TOTP]).
2. MFA ticket binding. Tickets issued by /login (and the Google callback)
were unbound — a stolen ticket replayed from a different origin still
worked. Tickets now carry SHA-256 hashes of the issuing request's IP
and User-Agent; redeemTicket rejects on mismatch. The ticket is burned
even on mismatch so a wrong-binding probe can't be retried.
3. TOTP replay within the same 30s step (RFC 6238 §5.2). The verifier
accepted the same code as many times as you submitted it. Now
verifyToken returns the matched counter, and /login/totp does a CAS
UPDATE on users.totp_last_counter — codes at counters <= the last
accepted value are rejected. New migration 030 adds totp_last_counter,
seeded on /totp/enable so the enrollment code itself can't be reused
at first login, and zeroed on /totp/disable.
4. Google OAuth domain check no longer falls back to the email suffix
when the hd (hosted-domain) claim is missing. Email-suffix matching
let consumer (non-Workspace) Google accounts whose email happens to
end in the allowed domain through; if GOOGLE_ALLOWED_DOMAIN is set,
the operator means "only this Workspace", so accounts without a
verified hd must be rejected.
Tests: new mfa-tickets.test.js covers ip/UA binding, single-use on
mismatch, and bindings-absent back-compat. totp.test.js updated for the
new verifyToken return shape (counter on success, null on failure;
truthiness still works at call sites) and adds an explicit
matched-counter check.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
