Credential Stuffing Defense: Stopping Automated Login Attacks at the Edge

Credential stuffing is not brute force. Attackers do not guess passwords — they test known username and password pairs leaked from other breaches against your login endpoint.

Because the credentials are real, traditional defenses like lockout after N failures are largely ineffective. A distributed attack across thousands of IPs never triggers per-IP limits.

Login must accept public traffic by definition. You cannot IP-allowlist it, and requiring users to solve a CAPTCHA on every attempt destroys conversion.

The effective window is narrow: you need to distinguish automated credential testing from a real user who forgot their password, without adding friction to the second group.

Running a trust check before the login handler executes means a blocked request never reaches your database, your session store, or your account lockout counter.

When the cost of each probe attempt rises — through challenges, delays, or silent drops — credential stuffing campaigns become economically unviable. Attackers move to easier targets.