File Browser provides a file managing interface within a specified directory and can be used to upload, delete, preview, rename, and edit files. Prior to version 2.55.0, the JSONAuth. Auth function contains a logic flaw that allows unauthenticated attackers to enumerate valid usernames by measuring the response time of the /api/login endpoint. The vulnerability exists due to a "short-circuit" evaluation in the authentication logic. When a username is not found in the database, the function returns immediately. However, if the username does exist, the code proceeds to verify the password using bcrypt (users.CheckPwd), which is a computationally expensive operation designed to be slow. This difference in execution path creates a measurable timing discrepancy. Version 2.55.0 contains a patch for the issue.