Credential Stuffing
Credential Stuffing is an attack where attackers use stolen username-password pairs from one breach to attempt login on other accounts. It exploits password reuse — the reality that users use the same password across multiple services.
# WHAT TEAMS RUN INTO
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Detection is harder than prevention. Credential stuffing looks like normal login traffic — someone with valid credentials trying to log in. Distinguishing between a legitimate user and an attacker using stolen credentials requires context and behavioral analysis.
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Credential stuffing is fast and cheap. Attackers can test millions of stolen passwords against a service in minutes using botnets. Defense systems get overwhelmed, and some attempts slip through.
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Breach notification creates a race condition. When a service is breached, attackers immediately use those credentials on other services before users can change their passwords. The window for damage is measured in minutes.
# WHY IT MATTERS
Credential Stuffing is a direct consequence of password reuse. If everyone used unique, strong passwords, credential stuffing would fail — a password from service A would be useless on service B. But humans reuse passwords for convenience, turning every breach into a multi-service compromise. Organizations cannot control whether users reuse passwords, but they can deploy MFA to stop credential stuffing from resulting in account takeover.