[6.4] user_privileges files aren't created if $root_directory doesn't end with a trailing slash
Let's say your config.inc.php has a root directory specified like this : $root_directory = '/var/www/vtiger';
/modules/Users/CreateUserPrivilegeFile.php (line 27) tries to open the user privileges file like this :
root_directory.'user_privileges/user_privileges_'.$userid.'.php',"w+");
And at line 116 for sharing privileges file :
root_directory.'user_privileges/sharing_privileges_'.$userid.'.php',"w+");
So the file full path will be /var/www/vtigeruser_privileges/user_privileges_X.php (same for sharing_privileges files) so they won't be created.
Each time the user will try to login, he'll get a blank page with "Sorry! Attempt to access restricted file".
Since there's a "@" before the fopen function, no error will be logged or displayed.