Broken authentication represents a significant security vulnerability where attackers exploit preventable gaps in authentication processes to gain unauthorized access to systems, as exemplified by the 2017 Equifax breach. Key causes include weak credential management, lack of multi-factor authentication (MFA), poor session management, and ineffective protection against automated attacks. Common attack methods include brute force, credential stuffing, session hijacking, and phishing, all of which can compromise sensitive information and result in severe repercussions for organizations. Preventative measures involve adopting passwordless authentication, enforcing strong passwords, implementing MFA, using password hashing, detecting breached passwords, and managing session vulnerabilities. These measures help mitigate the risk of broken authentication, ensuring that businesses can protect user data without compromising security or efficiency.