A missing authentication vulnerability in dulldusk/phpfm through 1.8.0 allows an unauthenticated remote attacker to access the full file manager functionality including reading, writing, deleting, and uploading files anywhere on the server filesystem. The authentication check in index.php at line 637 evaluates 'if ($auth_pass == '' || $loggedon==$auth_pass)', and since auth_pass is an empty string in the default configuration, the condition always evaluates to true and grants full access without credentials.