Froxlor is open source server administration software. Version 2.3.6 lets administrators configure "system.available_shells" as the approved shell list that customers may assign to FTP users. However, the server-side FTP account handlers do not enforce that whitelist when processing add or edit requests. As a result, an authenticated customer with shell delegation enabled can submit an arbitrary shell such as "/bin/bash" even when the panel UI only offers more restricted choices. In deployments that use the default "nssextrausers" integration, the attacker-controlled shell is then propagated into the system account database, leading to real host shell access. Version 2.3.7 fixes the issue.