We have previously wrote about Concrete CMS here. In that post we described how we managed to exploit a double race condition vulnerability in the file upload functionality in order to obtain remote command execution. In this blog post we will present multiple vulnerabilities in Concrete CMS that we have found at the end of last year during a pentest for one of our customers. For more info please see the “Mitigations” section regarding security tips for fixing the password poisoning issue and other tips on improving security for Concrete CMS.
Concrete CMS is designed for ease of use, for users with a minimum of technical skills. It enables users to edit site content directly from the page. It provides version management for every page, similar to wiki software, another type of web site development software. Concrete5 allows users to edit images through an embedded editor on the page. As of 2021, there are over 62,000 live websites that use Concrete CMS under the hood. During a recent pentest, our team found a very interesting vulnerability. Discovery of the vulnerability was relatively simple (a race condition), however creating a POC was quite challenging, hence the reason for this post. You will need a low privileged user to exploit this vulnerability and gain RCE in Concrete CMS.