Exponent CMS before 2.3.9 is vulnerable to an attacker uploading a malicious script file using redirection to place the script in an unprotected folder, one allowing script execution.
https://github.com/exponentcms/exponent-cms/releases/tag/v2.4.0
http://www.securityfocus.com/bid/94121
http://www.exponentcms.org/news/security-vulnerability-all-exponent-versions-june-2016