"Credential Stuffing Attack" is a less known and highly successful cyber-attack launched against web portals. It exploits the human behavior of re-using the passwords for ease to memorize and the weakness in defense technologies. A bad actor gets hold of user's credentials leaked from a website and tries the same set of credentials on different websites for further access on user's data. Traditional defense mechanism deployed by web portals fail to defend against this attack as it's a very silent, slow and evade the signature-based rules. Most of the small and medium scale web portals find it difficult to detect the attack.