Two problems with sign-count clone detection:
- suspicious_sign_count? flagged the case where both the stored and presented
counts are 0. Most synced passkeys (Apple/Google) report 0 every time, so every
legitimate sign-in was flagged — drowning real signals in noise. Per WebAuthn
§6.1.1 a 0 counter means "no counter"; only flag when BOTH counts are non-zero
and the new one does not advance.
- On a suspicious count the controller only logged a warning and then continued
to authenticate and overwrite the stored counter. A cloned credential therefore
worked indefinitely. webauthn_verify now rejects the sign-in (no session, no
counter update) and emails the user via a new SecurityMailer#suspicious_passkey_used.
Tests cover the corrected classification (synced/first-use/normal vs equal/
decreasing) and the new alert email.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Previously only TOTP-enabled triggered an email. Every other
security-relevant change — password change, TOTP disable, passkey
add/remove, API key create/revoke, email address change, backup-code
regeneration — happened silently, so an attacker on a stolen session
could quietly drop 2FA or hijack the email with no signal to the
account holder.
Add SecurityMailer with one method per event. Each email carries the
request IP, user-agent, and timestamp so the user can spot unfamiliar
activity. Email-address changes notify both the old and new addresses
with directional language; the old-address copy explicitly warns that
whoever made the change can now receive password reset emails.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
