Magento 2.1 prior to 2.1.19, Magento 2.2 prior to 2.2.10, Magento 2.3 prior to 2.3.3 uses weak cryptographic function to store the failed login attempts for customer accounts.Referenceshttps://magento.com/security/patches/magento-2.3.3-and-2.2.10-security-update
