A vulnerability has been identified regarding insufficient validation in the Frappe Cloud/ERPNext authentication process, which allows multiple email addresses to be accepted by manipulating the email field in the /api/method/press.api.account.signup endpoint. The vulnerability occurs when an unauthenticated remote attacker adds more than one email address. The service processes the entire value as a valid list of recipients and sends the OTP code to all addresses without proper validation of all added emails (only one of them needs to be valid). Exploiting this vulnerability would allow an attacker to: * Obtain the authentication OTP; * Impersonate someone else in the registration process; * Register accounts using other people's email addresses without access to the mailbox; * Indirectly confirm the existence of already registered email addresses.