Pre-Auth Risk Scoring Can Stop Credential Stuffing Before Password Checks Begin

Credential stuffing attacks use large lists of leaked email-password pairs, replaying them across thousands of IPs at low volume to evade traditional defenses. Standard countermeasures like per-account lockout and per-IP rate limiting both fail because attackers deliberately spread attempts thin across many accounts and residential proxies. A more effective approach involves scoring each login request before any password verification occurs, using the IP address and email address as cheap risk signals. Datacenter IPs, known proxy exits, and emails appearing on abuse lists can flag suspicious requests without touching the expensive bcrypt hash. By tiering responses based on a combined risk score, servers can reject or challenge likely bot traffic before wasting CPU on junk authentication attempts.