How to Detect Credential Stuffing Attacks in Your Nginx Logs

How to Detect Credential Stuffing Attacks in Your Nginx Logs Credential stuffing is when attackers take leaked username/password lists from data breaches and try them automatically against your login endpoint. Unlike brute force (guessing random passwords), credential stuffing uses real credentials — which makes it far more dangerous and harder to spot. The good news: it leaves a very clear pattern in your nginx logs. What Credential Stuffing Looks Like A normal login attempt looks like this: 192.168.1.1 - - [20/Mar/2026:09:15:00 +0000] "POST /api/login HTTP/1.1" 200 156 A credential stuffing attack looks like this: 185.220.101.34 - - [20/Mar/2026:09:15:01 +0000] "POST /api/login HTTP/1.1" 401 53 185.220.101.34 - - [20/Mar/2026:09:15:02 +0000] "POST /api/login HTTP/1.1" 401 53 185.220.101.34 - - [20/Mar/2026:09:15:02 +0000] "POST /api/login HTTP/1.1" 401 53 185.220.101.34 - - [20/Mar/2026:09:15:03 +0000] "POST /api/login HTTP/1.1" 401 53 185.220.101.34 - - [20/Mar/2026:09:15:03 +0000]