Enumeration attacks: By providing specific error messages like "Email not found," the application is revealing information about its database. An attacker can systematically try different email addresses. If they get an Email not found message, they know that email isn't registered. If they get a different error (like Incorrect password), they know the email is registered and can then focus on trying to guess the password. This process of elimination is called enumeration.
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A) Credential stuffing attacks: These attacks rely on using lists of known username/password combinations obtained from data breaches on other sites. While a successful enumeration could prepare for a credential stuffing attack by identifying valid usernames, the error message itself doesn't directly enable credential stuffing.
B) Cross-site scripting (XSS) attacks: XSS attacks involve injecting malicious scripts into websites viewed by other users. The error message "Email not found" doesn't provide an injection point for scripts.
D) SQL injection attacks: These attacks exploit vulnerabilities in database queries to inject malicious SQL code. While poor input validation could lead to SQL injection, the specific error message "Email not found" doesn't directly indicate such a vulnerability. The error message is displayed after the database query has been executed.