The patch for directory traversal (CVE-2017-5480) in b2evolution version 6.8.4-stable has a bypass vulnerability. An attacker can use ..\/ to bypass the filter rule. Then, this attacker can exploit this vulnerability to delete or read any files on the server. It can also be used to determine whether a file exists.

Directory traversal vulnerability in inc/files/files.ctrl.php in b2evolution through 6.8.3 allows remote authenticated users to read or delete arbitrary files by leveraging back-office access to provide a .. (dot dot) in the fm_selected array parameter.