source: https://www.securityfocus.com/bid/61196/info

Apache Struts is prone to multiple open-redirection vulnerabilities because the application fails to properly sanitize user-supplied input.

An attacker can leverage these issues by constructing a crafted URI and enticing a user to follow it. When an unsuspecting victim follows the link, they may be redirected to an attacker-controlled site; this may aid in phishing attacks. Other attacks are possible.

Apache Struts 2.0.0 prior to 2.3.15.1 are vulnerable. 

http://www.example.com/struts2-showcase/fileupload/upload.action?redirect:http://www.example.com/
http://www.example.com/struts2-showcase/modelDriven/modelDriven.action?redirectAction:http://www.example.com/%23