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List:       full-disclosure
Subject:    [FD] MS Made Simple - File upload bypass with .phar extension lead to RCE
From:       riccardo krauter <riccardo.krauter () gmail ! com>
Date:       2021-03-17 13:22:10
Message-ID: 8a2e062b-77ae-4969-f38b-640532e2b7e5 () gmail ! com
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1) Summary

Affected software  CMS Made Simple-2.2.15
Vendor URLhttp://www.cmsmadesimple.org/  <http://www.cmsmadesimple.org/>
Vulnerability	   File upload bypass with .phar extension lead to RCE

2) Vulnerability Description

The vulnerability affect the `FilePicker` module,
it is possible to bypass the restriction and upload a malicious file with `.phar` extension to \
gain Remote Code Execution. This vulnerability is remotely exploitable and require \
authentication.  
3) PoC and details

* Login into the admin area and surf to the `MicroTiny WYSIWYG editor` functionality then click \
                on the insert/edit image button
* A new window will be opened, now click on the search button, the `CMSMS File Picker` will be \
                shown
* Click on the upload button and Select the .phar file
* Surf to uploads/your-file-name.phar and enjoy the shell

The exploit is working because the upload handler checks only if the extension contains the \
`php` string (obviously `phar` does not match). The exploit works fine on a standard Ubuntu \
system, here the configuration used for the tests:

* Linux ubuntu 5.4.0-58-generic
* php version 7.4.3
* Apache/2.4.41 (Ubuntu)
* File Picker version = "1.0.5"
* CMS Made Simple-2.2.15

More details here: https://github.com/beerpwn/CVE/blob/master/cms_made_simple_2021/file_upload_RCE/File_upload_to_RCE.md


4) Credits

This vulnerability has been discovered and reported
by Riccardo Krauter researcher @ Soter IT Security (soteritsecurity.com).

5) Timeline

2021/02/26  Vendor was informed
2021/02/26  Vendor said he won't fix
2021/03/17  Public disclosure


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