Enumeration of unauthenticated users in FacturaScripts, version 2025.61. The application returns different responses when attempting to log in with a valid username compared to an invalid one. An unauthenticated attacker could systematically identify valid usernames by examining variations in the application’s responses, such as changes in response time, discrepancies between error messages or differences in HTTP status codes. A successful exploit allows the attacker to compile a list of valid user accounts. This list could be used to carry out targeted brute-force attacks, password spraying, credential stuffing or social engineering campaigns against the confirmed accounts.