Credential stuffing is an attack method where cybercriminals use previously stolen credentials (usernames and passwords) to gain unauthorized access to many different accounts. Because attackers understand that many people reuse passwords across multiple sites, attackers can attempt large-scale automated login attempts to breach user accounts. The success of this attack relies on the high likelihood that users often use the same credentials for multiple platforms.
Example:
An attacker uses a list of usernames and passwords stolen in a previous data breach (e.g., from a social media platform) to gain access to a variety of accounts, such as email, bank accounts, or online shopping profiles. Even though the login attempts may be blocked on one platform due to account lockouts, attackers often find success on less secure sites where users have reused their credentials.